TIN(IV) CHLORIDE 1
Tin(IV) Chloride is present as an external Lewis acid. As a consequence, four im-
portant experimental variables must be considered when using
SnCl4 as a promoter: (1) the stoichiometry between the substrate
SnCl4
and the Lewis acid; (2) the reaction temperature; (3) the nature of
the Lewis base site(s) in the substrate; and (4) the order of addi-
[7646-78-8] Cl4Sn (MW 260.51) tion. These variables influence the reaction pathway and product
distribution.5
InChI = 1/4ClH.Sn/h4*1H;/q;;;;+4/p-4/f4Cl.Sn/h4*1h;/q4*-1;m
InChIKey = HPGGPRDJHPYFRM-LUCXXLOKCB
SnR3 SnCl3
+ SnCl4 + SnBu3Cl (1)
(strong Lewis acid used to promote nucleophilic additions,
OTMS O
pericyclic reactions, and cationic rearrangements; chlorination
+ SnCl4 + TMSCl (2)
SnCl3
reagent) R R
Alternate Name: stannic chloride.
ć% ć%
Physical Data: colorless liquid; mp -33 C; bp 114.1 C; d 2.226
Nucleophilic Additions to Aldehydes. SnCl4 is effective
gcm-3.
in promoting the addition of nucleophiles to simple aldehydes.
Solubility: reacts violently with water; sol cold H2O; dec hot
Among the most synthetically useful additions are allylstannane
H2O; sol alcohol, Et2O, CCl4, benzene, toluene, acetone.
and -silane additions. The product distribution in the stannane re-
Form Supplied in: colorless liquid; 1 M soln in CH2Cl2 or hep-
actions can be influenced by the order of addition, stoichiometry,
tane; widely available.
and reaction temperature. The anti geometry of the tin aldehyde
Purity: reflux with mercury or P2O5 for several hours, then dis-
complex is favored due to steric interactions. Furthermore, the six-
till under reduced nitrogen pressure into receiver with P2O5.
coordinate 2:1 complex is most likely the reactive intermediate in
Redistill. Typical impurities: hydrates.
these systems. The use of crotylstannanes provides evidence for
Handling, Storage, and Precaution: hygroscopic; should be
competing transmetalation reaction pathways (eq 3).6 Superior
stored in a glove box or over P2O5 to minimize exposure to
selectivities are provided by Titanium(IV) Chloride.
moisture. Containers should be flushed with N2 or Ar and tightly
O
sealed. Perform all manipulations under N2 or Ar. Solvating
OH
SnBu3
with H2O liberates much heat. Use in a fume hood.
H
R
Lewis acid
normal addition 1.3 equiv SnCl4 22.8
inverse addition 1.3 equiv SnCl4 21.8
normal addition 1.05 equiv TiCl4 90.5
Original Commentary
inverse addition 2.1 equiv TiCl4 4.4
Stephen Castellino
OH
OH
Rh�ne-Poulenc Ag. Co., Research Triangle Park, NC, USA OH
+++ (3)
R
David E. Volk R
R
North Dakota State University Fargo, ND, USA
26.0 36.4 14.8
74.9 1.2 2.2
Introduction. SnCl4 is used extensively in organic synthe-
7.0 2.1 0.5
sis as a Lewis acid for enhancing a variety of reactions. SnCl4
90.8  4.9
is classified as a strong Lewis acid according to HSAB theory,
and therefore interacts preferentially with hard oxygen and ni- The presence of additional Lewis base sites within the molecule
trogen bases. Six-coordinate 1:2 species and 1:1 chelates are the can result in the formation of chelates with SnCl4 or TiCl4, which
most stable coordination complexes, although 1:1 five-coordinate can lead to 1,2- or 1,3-asymmetric induction with the appropriate
species are also possible.1 SnCl4 can be used in stoichiometric substitution at the C-2 or C-3 centers. NMR studies have pro-
amounts, in which case it is considered a  promoter , or in substo- vided a basis for explaining the levels of diastereofacial selectiv-
ichiometric amounts as a catalyst, depending upon the nature of ity observed in nucleophilic additions to Lewis acid chelates of
the reaction. SnCl4 is an attractive alternative to boron, aluminum, �-alkoxy aldehydes with substitution at the C-2 or C-3 positions.7
and titanium Lewis acids because it is monomeric, highly soluble These studies reveal that SnCl4 chelates are dynamically unsta-
in organic solvents, and relatively easy to handle. SnCl4 and TiCl4 ble when substrates are sterically crowded at the alkoxy center,
are among the most common Lewis acids employed in  chelation thus enhancing the formation of 2:1 complexes and/or competing
control strategies for asymmetric induction. However, SnCl4 is metathesis pathways. Furthermore, for �-siloxy aldehydes, the 2:1
not often the Lewis acid of choice for optimum selectivities and SnCl4 complex is formed preferentially over the corresponding
yields. chelate.8
SnCl4 is also the principal source for alkyltin chlorides,
RnSnCl4 - n.2 Allyltrialkyltin reagents react with SnCl4 to pro- Mukaiyama Aldol Additions. Lewis acid-promoted addi-
duce allyltrichlorotin species through an SE2 pathway (eq 1).3 tions of a chiral aldehyde to a silyl enol ether or silyl ketene
Silyl enol ethers react with SnCl4 to give ą-trichlorotin ketones (eq acetal (the Mukaiyama9 aldol addition) occurs with good diastere-
2).4 Transmetalation or metathesis reactions of this type are com- ofacial selectivity.10 The reaction has been investigated with non-
peting pathways to nucleophilic addition reactions where SnCl4 heterosubstituted aldehydes, ą- and �-alkoxy aldehydes,11 ą- and
Avoid Skin Contact with All Reagents
2 TIN(IV) CHLORIDE
�-amino aldehydes,12 and thio-substituted aldehydes.13 High di- presence of a leaving group on the silane is essential for good selec-
astereoselectivity is observed in the SnCl4- or TiCl4-promoted al- tivity since the reaction proceeds intramolecularly through a 2-O-
dol addition of silyl enol ethers to ą- and �-alkoxy aldehydes. Prior organosilyl glycoside. The availability of furanosides in the ribo,
chelation of the aldehyde before addition of the enol silane is im- xylo, and arabino series make this reaction valuable for the stereos-
portant because certain enol silanes interact with SnCl4 to produce elective synthesis of C-furanosides. Regioselective glycosylation
ą-trichlorostannyl ketones, which provide lower selectivity.14 of nitrogen-containing heterocycles is also effectively promoted
Simple diastereoselectivity is independent of the geometry of by SnCl4, and has been used in the synthesis of pentostatin-like
the enol silane, and the reaction does not proceed through prior nucleosides, such as (1).19
Si Ti or Si Sn exchange. Good anti selectivities (up to 98:2)
SiMe2Cl
are obtained in the SnCl4-promoted reactions of chiral ą-thio- RO
OR
SnCl4
substituted aldehydes only with ą-phenylthio-substituted aldehy-
O
OMe
+
des (eq 4). Stereorandom results are obtained with SnCl4 when
OH
other alkylthio-substituted aldehydes, such as ą-isopropylthio-
substituted aldehydes, are used. Boron Trifluoride Etherate catal-
RO
ysis gives better anti selectivities than SnCl4 for aldehydes
OR
O
with smaller alkylthio substituents. Excellent syn selectivities are (7)
obtained for ą-thio-substituted aldehydes with TiCl4.
OH
R1S
OMe
Lewis acid
+
R
HO
OTMS
O
N
NH
R = H: pentostatin
HO
R1S R1S
N
R = OH: coformycin
N
O
+ (4)
R CO2Me R CO2Me
OH OH
syn anti OH
(1)
Additions to Nitriles. SnCl4-promoted addition of malonates
Selective De-O-benzylation. Regioselective de-O-
and bromomalonates to simple nitriles (not electron deficient)
benzylation of polyols and perbenzylated sugars is achieved
gives ą,�-dehydro-�-amino acid derivatives (eq 5).15 SnCl4 is
with organotin reagents or other Lewis acids.20,21 The
the Lewis acid of choice for the condensation of aroyl chlorides
equatorial O-benzyl group of 1,6-anhydro-2,3,4-tri-O-benzyl-�-
with sodium isocyanate, affording aroyl isocyanates in 70 85%
D-mannopyranose is selectively cleaved by SnCl4 or TiCl4 (eq
yields.16 Nonaromatic acyl chlorides react under more variable
8).2 The equatorial O-benzyl group is also selectively cleaved
reaction conditions.
when one of the axial O-benzyl groups is replaced by an O-methyl
O O
RO2C
group. The 2-O-benzyl group of 1,2,3-tris(benzyloxy)propane is
1. SnCl4
+ EtCN (5)
selectively cleaved (eq 9), but no debenzylation is observed with
RO OR
2. Na2CO3
RO2C NH2
1,2-bis(benzyloxy)ethane.
55%
Rearrangement of Allylic Acetals. Lewis acid-promoted
Hydrochlorination of Allenic Ketones. SnCl4 is also a source (SnCl4 or Diethylaluminum Chloride) rearrangements of allylic
for generating chloride anions which form new carbon chlorine acetals provide substituted tetrahydrofurans.22 Upon addition of
bonds. This occurs through a ligand exchange pathway which Lewis acid, (2) rearranges to the all-cis furan (3) (eq 10). No
has been exploited in the formation of �-chloro enones from racemization is observed with optically active allylic acetals; how-
conjugated allenic ketones (eq 6).17 Yields range from 36 82% ever, addition of KOH completely epimerizes the furan carbonyl
with complete selectivity for the trans geometry. A variety of bond, as does quenching at room temperature. Acetals suc-
substituents (R1, R2) can be tolerated including aryl, rings, and cessfully undergo similar rearrangement provided the alkene is
alkoxymethyl groups (R1). substituted. Completely substituted tetrahydrofurans are synthe-
sized stereoselectively (<97% ee) by the rearrangement of dis-
Cl
ubstituted allyl acetals (eq 11). This reaction is related to the
"
SnCl4, 20 �C
R1 R2 R1 R2 (6) acid-catalyzed rearrangements of 5-methyl-5-vinyloxazolidines
benzene
O O
to 3-acetylpyrrolidines, which involves an aza-Cope rearrange-
ment and Mannich cyclization.23
O O
Glycosylations. The reaction of glycofuranosides having a
OBn OBnO OH
0.5 h
+ (8)
free hydroxyl group at C-2 with functionalized organosilanes, O O O
OBn OH OBn
in the presence of SnCl4, provides C-glycosyl compounds in
OBn OBn OBn
high stereoselectivity (eq 7).18 Organosilanes such as 4-(chlorodi-
5%
SnCl4 92%
methylsilyl)toluene, chlorodimethylvinylsilane, Allyltrimethylsi-
19%
TiCl4 77%
lane, and allylchlorodimethylsilane are effective reagents. The
A list of General Abbreviations appears on the front Endpapers
TIN(IV) CHLORIDE 3
OBn OBn
SnCl4
This reaction is useful for cyclizations involving 6-endo-
(9)
OBn OH
trigonal (eq 14) and  allowed 7-endo trigonal processes (eq 15),
86%
OBn OBn
but not for those involving 5-endo trigonal processes (eq 16).
These observations are consistent with the Baldwin rules.
O
O
SnCl4,  70 �C
O
Ph (10) O
O  10 �C, 2 h
CO2Me
CO2Me
SnCl4
58% O Ph
(15)
(2) (3)
62%
O
R1
O
R2 SnCl4,  70 �C
O R2
(11)
CO2Me
 10 �C, 2 h
R1
O
O
O
CO2Me
SnCl4
R1 = Me, R2 = H; 90% (16)
CO2Me
R1 = H, R2 = Me; 73%
The rearrangement is also useful for furan annulations, through O
enlargement of the starting carbocycle.24 Thus addition of SnCl4
to either diastereomer of the allylic acetal (4) produces the cis-
fused cycloheptatetrahydrofuran (5) in 48 76% yield (eq 12).
Reactions involving 4- and 6-exo trigonal cyclizations result in
Acetals derived from trans-diols rearrange to the same cis-fused
poor yields or undesired products, while those involving 5-exo
bicyclics in higher yield. The stereochemistry of a terminal alkene
trigonal cyclizations produce higher yields (eq 17). This synthetic
is transmitted to the C-3 carbon of the bicyclic products (eq
strategy can also be used to form bicyclic and spiro compounds
13). Rearrangements of acetals require substitution at the inter-
(eqs 18 and 19).
nal alkene carbon.
O O
O
H
CO2Me
O
SnCl4,  70 �C CO2Me
SnCl4
R
R (12)
(17)
O
1 h
O 66%
48 76%
H
(4) (5)
O
O
CO2Et
CO2Et
R1
SnCl4
O R1
(18)
R2
R2 SnCl4,  70 �C
61%
R
(13)
O
1 h
R
O
56 81%
O
H
O
O
CO2Et
SnCl4
EtO2C
(19)
ą-tert-Alkylations. SnCl4-promoted ą-t-alkylations of
63%
alkenyl �-dicarbonyl compounds is a particularly useful cycliza-
tion reaction.25 Cyclization occurs through initial formation of a
stannyl enol ether, followed by protonation of the alkene to form
a carbocation which undergoes subsequent closure (eq 14). The
analogous ą-s-alkylation reactions are best catalyzed by other
Alkene Cyclizations. Cationic cyclizations of polyenes, con-
Lewis acids.
taining initiating groups such as cyclic acetals, are promoted by
Cl3Sn SnCl4 and have been utilized in the synthesis of cis- and trans-
O O
O O
decalins, cis- and trans-octalins, and tri- and tetracyclic terpenoids
SnCl4
R
R + HCl
and steroids.26 In most instances, all-trans-alkenes yield products
with trans,anti,trans stereochemistry (eq 20), while cis-alkenes
lead to syn stereochemistry at the newly formed ring junctions.
The stereoselectivity of polyene cyclizations are often greatly di-
Cl3Sn
minished when the terminating alkene is a vinyl group rather than
O O
O O
an isopropenyl group. Acyclic compounds which contain termi-
R + SnCl4 (14)
R
nal acyclic acetals and alkenes or vinylsilanes can be cyclized in
+ a similar fashion to yield eight- and nine-membered cyclic ethers
Cl
(eq 21).27
Avoid Skin Contact with All Reagents
4 TIN(IV) CHLORIDE
O O
TMS
O O
SnCl4
H
SnCl4
(24)
CO2Et
pentane, 0 �C
63%
O O
CO2Et
H H (20)
R
34%
R
H
O
O
O
OH
Polymerization. Cationic polymerizations are catalyzed by
SnCl4 and other Lewis acids (eq 25). Propagation is based upon the
formation of a cationic species upon complexation with SnCl4.30
R1 R
Cl
Radical pathways are also possible for polymer propagation.31
2 equiv SnCl4
 20 �C, 13 h
+ (21)
83%
HB
RO
O O OR
O
(25)
OR2 SnCl4
n
R1 = H, TMS; R2 = (CH2)2OMe
The analogous cyclization of chiral imines occurs in high yields
Diels Alder Reactions. Diels Alder reactions are enhanced
(75 85%) with good asymmetric induction (36 65% ee).28 For
through the complexation of dienophiles or dienes by Lewis
example, the cyclization of aldimine (6), derived from methyl
acids.32 Furthermore, Lewis acids have been successfully em-
citronellal, using SnCl4 affords only the trans-substituted
ployed in asymmetric Diels Alder additions.33 Although SnCl4
aminocyclohexane (7) in high yield (eq 22). Exo products are
is a useful Lewis acid in Diels Alder reactions, in most in-
formed exclusively or preferentially over the thermodynamically
stances titanium or aluminum Lewis acids provide higher
favored endo products.
yields and/or selectivities. The stereoselectivity in Lewis acid-
promoted Diels Alder reactions between chiral ą,�-unsaturated
N-acyloxazolidinones shows unexpected selectivities as a function
Ph of the Lewis acid (eq 26).34 Optimum selectivity is expected for
SnCl4
(22)
chelated intermediates, yet both SnCl4 and TiCl4 perform poorly
N
N
84%
H relative to Et2AlCl (1.4 equiv). The formation of the SnCl4 N-
Ph
acyloxazolidinone chelate has been confirmed by solution NMR
(6) (7)
studies.35 These data suggest that other factors such as the steric
bulk associated with complexes may contribute to stereoselectiv-
ity.
SnCl4-induced cyclizations between alkenes and enol acetates
In Lewis acid-promoted Diels Alder reactions of cyclopent-
result in cycloalkanes or bicycloalkanes in high yield (eq 23). It is
adiene with the acrylate of (S)-ethyl lactate, good diastereofa-
interesting to note that the TMSOTf-catalyzed reaction can yield
cial and endo/exo selectivity are obtained with SnCl4 (84:16;
fused products rather than bicyclo products. Alkenic carboxylic
endo/exo = 18:1) and TiCl4 (85:15; endo/exo = 16:1).36 It is inter-
esters, allylic alcohols, sulfones, and sulfonate esters are also cy-
esting to note that boron, aluminum, and zirconium Lewis acids
clized in the presence of SnCl4; however, alkenic oxiranes often
give the opposite diastereofacial selectivity (33:67 to 48:52). Com-
cyclize in poor yield.26a
peting polymerization of the diene is observed in methylene chlo-
ride, particularly with TiCl4, but not in solvent mixtures containing
O
n-hexane.
SnCl4
O
98%
+
X
RO2C COX
Lewis acid XOC
OAc
(23)
exo I exo II
CO2R
(26)
TMSOTf
O
65%
N O
X =
CO2R
+ +
COX
XOC
endo I endo II
SnCl4 is also effective in the opening of cyclopropane rings to
Lewis acid conv % Łendo:Łexo endo I:endo II
produce cationic intermediates useful in cyclization reactions. For
example, the cyclization of aryl cyclopropyl ketones to form aryl
1.1 equiv SnCl4 70 3.1
14.9
tetralones, precursors of aryl lignan lactones and aryl naphthalene
1.1 equiv TiCl4 100 2.7
9.9
1.4 equiv Et2AlCl 100 17
lignans, is mediated by SnCl4 (eq 24).29 The reaction is success-
50.0
ful in nitromethane, but not in benzene or methylene chloride.
Analogous cyclizations with epoxides result in very low yields Cycloalkenones generally perform poorly as dienophiles in
(2 5%). Diels Alder reactions but their reactivity can be enhanced by
A list of General Abbreviations appears on the front Endpapers
TIN(IV) CHLORIDE 5
O
Lewis acids.37 SnCl4 is effective in promoting the Diels Alder
SnCl4
t-Bu
reaction between simple 1,3-butadienes, such as isoprene and
+
N R
piperylene, and cyclopentenone esters. For example, the SnCl4-
promoted cycloaddition between (8) and isoprene is completely
O
regioselective, providing the substituted indene in 86% yield (eq
(9)
O
O
H
H
27).38 However, cycloaddition does not occur in the presence of
t-Bu
SnCl4 when the diene contains an oxygen-bearing substituent such + (29)
R N
R N
as an alkoxy or siloxy group. In these cases, as is generally true t-Bu
H
H
O
Ph O
for the Diels Alder reactions of cycloalkenones, other Lewis acids
R =
(10) (11)
are more effective. For example, SnCl4-promotion of the cycload-
dition between (8) and 3-methyl-2-(t-butyldimethylsiloxy) buta-
diene yields 37% of the desired product, while Zinc Chloride
provides a 90% yield. When furan or 2-methyl-1-alkylsiloxybut- O
OH
OTMS
adiene are utilized as dienes, only decomposition of the starting
X SnCl4
+ (30)
material is observed with SnCl4.
X
CHO
O O
CO2Me
X = O, CH2
SnCl4
CO2Me
+ (27)
O
H
OTMS
OMe
(8)
X SnCl4
OMe
+ (31)
X
The Lewis acid-promoted Diels Alder reaction has been em- OMe
ployed in the assembly of steroid skeletons.39 The cycloaddition
reaction between a substituted bicyclic diene and 2,6-dimethyl-
[3 + 2] Cycloadditions. Lewis acid-mediated [3 + 2] cycload-
benzoquinone produces two stereoisomers in a 1:5 ratio with a
ditions of oxazoles and aldehydes or diethyl ketomalonate have
yield of 83% when SnCl4 is used in acetonitrile. TiCl4 provides
been observed using organoaluminum and SnIV Lewis acids.45
slightly higher selectivities (1:8) but lower yield (70%) (eq 28).
The reactions are highly regioselective, with stereoselectivity ex-
When the dienophile N-ą-methylbenzylmaleimide (9) is re-
tremely dependent upon Lewis acid (eq 32). For example, the
acted with 2-t-butyl-1,3-butadiene in the presence of Lewis acids,
(BINOL)AlMe-promoted reaction between benzaldehyde and the
cycloadducts (10) and (11) are formed (eq 29).40 While SnCl4 pro-
oxazole (12) provides the oxazoline with a cis/trans ratio of
vides (10) and (11) in a 5:1 ratio, TiCl4 and EtAlCl2 both provide
98:2. The selectivity is reversed with SnCl4 which provides a
a 15:1 ratio. Polymerization of the diene competes with adduct
cis/trans ratio of 15:85. trans-5-Substituted 4-alkoxycarbonyl-2-
formation under all conditions.
oxazolines are synthesized under thermodynamic conditions in
[4 + 3] Cycloadditions. Oxyallyl cations,41 which react as C3 the aldol reaction of isocyanoacetates with aldehydes.46
rather than C2 components in cyclization reactions, are gener-
CO2Me
Lewis acid
ated by the addition of SnCl4 to substrates which contain silyl N N
(32)
enol ethers which are conjugated with a carbonyl moiety. Thus 2-
OMe
Ar Ar
PhCHO Ph
O O
(trimethylsiloxy)propenal undergoes cyclization with cyclopenta-
(12)
diene or furan (eq 30).42 Substituted 1,1-dimethoxyacetones also
form these intermediates and undergo subsequent cyclizations (eq
31).43 This method complements the usual synthesis of oxyallyl
[2 + 2] Cycloadditions. The regioselectivity in the cy-
cations involving reductive elimination of halogens from halo-
cloaddition reactions of 2-alkoxy-5-allyl-1,4-benzoquinones with
genated ketones or electronically equivalent structures.44
styrenes is controlled by the choice of TiIV or SnCl4 Lewis acids
(eq 33).47 The use of an excess of TiCl4 or mixtures of TiCl4 and
O
Ti(O-i-Pr)4 produces cyclobutane (13) as the major or exclusive
Lewis acid
product, while SnCl4 promotion with one equivalent of Lewis acid
+
MeCN
results in the formation of (14) only. These reactions represent a
HO
classic example of the mechanistic variability often associated
O
with seemingly modest changes in Lewis acid.
O
O
Ene Reactions. The Lewis acid-catalyzed ene reaction is syn-
thetically useful methodology for forming new carbon carbon
H
H
bonds.48 Ene reactions utilizing reactive enophiles such as formal-
+ (28)
H
H
dehyde and chloral can be promoted by SnCl4. SnCl4 also
O
O
HO
HO
enhances intramolecular ene reactions, such as the cyclization of
(15) which produces the ą-hydroxy �-lactone in 85% yield (eq
SnCl4 1:5
34).49 The ene cyclization of citronellal to give isopulegol has
TiCl4 1:8
also been reported.50 Proton scavenging aluminum Lewis acids
Avoid Skin Contact with All Reagents
6 TIN(IV) CHLORIDE
1. SnCl4
such as RAlCl2 are most often used in ene reactions to eliminate
Bu3Sn
2. RCHO
proton-induced side reactions.
OBn
16
O
HO
HO
Ar
+ (35)
R BnO
R BnO
OR
O syn:anti 95:5
H
O
OR
(13)
Lewis acid
+ (33)
1. SnCl4
 78 �C
Bu3Sn
2. RCHO
O
X
O H
OTBDMS
Ar
OR
17
X = H, 3,4-(OMe)2, 3,4-(-OCH2O-);
R = Me, R = Bn
OH
HO
OTBDMS
O
+ (36)
R
R TBDMSO
(14)
syn:anti 30:60
O
O CHO
OH
SnCl4
Allylstannane (16) also adds to activated imines with high
(34)
stereofacial selectivity with preference for anti addition and the
85%
formation of the E double bond, while addition of the TBDMS
protected stannane (17) takes place with the opposite stereofacial
(15)
selectivity (eq 37).56,58
SnCl4
16 or 17
R2 2
CO2R2 N
R2 2
First Update R2 2
HN OR HN OR
(37)
+
Calvin J. Chany II
R2 O2C R2 O2C
Barnstead International, Dubuque, IA, USA
1,5-syn 1,5-anti
&
Rush University Medical Center, Chicago, IL, USA
Stannane R R2 R2 2 Yield (%) 1,5-syn 1,5-anti
Nucleophilic Additions to Aldehydes. Stereodirected addi-
C4H9 CHPh2 79 10 90
16 Bn
tions of allyltributylstannanes to aldehydes with promotion by
CHPh2 91 75 25
17 TBDMS C4H9
SnCl4 are possible when the stannane also contains an alkoxy
group; for example, the reaction of aldehydes with 4-alkoxypent-
2-enenyl tributylstannanes (16) afford high yields of 1,5-syn Directed additions involving 1,6- (eq 38),59 1,7- (eq 39),60 and
61
addition products.51-53 Typical reactions involve combining the 1,8- stereoinduction have also been reported. The 1,8-induction
ć%
stannane with SnCl4 at -78 C for 5 min in dichloromethane fol- is not direct, but has foundation on a 1,5-asymmetric induction
lowed by the addition of the aldehyde. The use of other Lewis to afford an intermediate that when derivatized is subjected to
acids led to competing decomposition.53,54 With benzyl protec- an Ireland-Claisen rearrangement. Interestingly the 1,6- and 1,7-
tion the stereofacial selectivity was found to be independent of the directed additions give better or more consistent reaction prod-
aldehyde used whether achiral or chiral (eq 35). ucts with the use of tin(IV) bromide (eqs 38 and 39). In these
ą-Hydroxyaldehydes, however, are an exception to this rule. two examples the hydroxyl groups in the starting stannanes were
Addition of S-16 to R-2-hydroxypropanal proceeds with nor- unprotected.
mal syn:anti stereofacial selectivity, whereas addition to the S-
aldehyde yields a mixture of syn:anti products.52,53,55 The loss of
OH
SnBr4
stereocontrol in this case is attributed to the  mismatching of the
Bu3Sn CH3 PhCHO
chiral aldehyde and chiral stannane. The reactions are conceived to
proceed via a coordinated tin complex with the size of the alkoxy
protecting group dictating the intermediacy of 5- or 6-coordinate
HO OH
tin complexes.52,56,57 Changing the 4-alkoxy protecting group
1,6-anti-isomer
+ (38)
from Bn (16) to the bulky TBDMS (17) leads to a preference for
Ph CH3
1,5-anti addition products with E double bond formation and some
syn:anti 96:4
loss of selectivity (eq 36).
A list of General Abbreviations appears on the front Endpapers
TIN(IV) CHLORIDE 7
H
CH3 SnBr4
Bu3Sn
M
PhCHO
O
OH
LA
N
O
HO PMP
1,7-anti-isomer (39)
+
HO HO
Ph CH3
H H
HO
syn:anti 90:10
+ (41)
N N
O
O
PMP PMP
syn anti
The usefulness of these directed additions is demonstrated in
the synthesis of the macrodiolide pamamycin-607,62 which is
LA
M syn anti Yield (%)
reported to have interesting antifungal properties. Further ex-
SnCl4 92 8 79
SiMe3
ploitation is demontrated by the use of L-quebrachitol as a chi-
BF3-Et2O
SnBu3
91 9 75
ral auxilary in SnCl4 mediated additions of silyl enol ethers to
ą-keto esters affording chiral teriary alcohols in high yields and
with excellent diasteriomeric excess.63
O O
O O
Trimethylsilylalk-2-enes also add to aldehydes in the presence
OH
SiMe3
O
of SnCl4, however, the transmetallation is considerably slower
(42)
SnCl4
when compared to the tributylstannanes (1 2 h vs. 5 min at
N N
ć%
-78 C), which leads to lower yields and loss of stereoselectivity
O R2 O R2
(eq 40).64
NH2
RCO2R2
RCNSnCl4
SnCl4
BnO Si(CH3)3
CH2(COOR2 )2
N O
PhCHO
NH2
CH3
H
(43)
OH OH
+ (40)
NH2
BnO CH3 BnO CH3
RCN
RCO2CH3
SnCl4
CH3COCH2CO2CH3
NH2
N CH3
H
Reaction time Yield (%) syn/anti
(44)
20 min 13 23/77
Similarly, reactions of �-enaminonitriles offer entry into the 4-
1 h 65 15/85
aminopyridone (eq 45) or 4-aminopyridine (eq 46) heterocyclic
2 h 67 14/86
cores.70
NH2
CO2R2
CN
SnCl4
The coupling of 4-alkoxy-2-trimethylsilyl-2-enyl(tributyl)
(45)
stannanes with aldehydes affords a template for the stereocon-
CH2(CO2R2 )2
Y
O
Y
N
NH2
trolled preparation of 1,3,5-triols with excellent yields.65 Addi-
H
tion reactions have also been reported in the functionalization of
Y = -CH2-, -CH2CH2-
azetidinone-2-carbaldehydes.66-68 Allylsilane and allylstannane
additions to these aldehydes both give high yields of the syn ad-
CN
SnCl4
dition products when the reactions are catalyzed by Lewis acids
CH3COCH2CO2CH3
(LA) (eq 41).
Y
NH2
Similar reactions were observed with of azetidin-2,3-diones,
which gave high yields of the homolallylic alcohols (eq 42).67,68
NH2
Y = -CH2-, -CH2CH2-
CO2CH3
Addition to Nitriles. The SnCl4 mediated addition of �-
(46)
dicarbonyl compounds to nitriles affords dicarbonyleneamine in-
Y
CH3
termediates, which offer entry into substituted heterocyclic cores. N
Reactions involving ortho-aminobenzonitriles lead to the forma-
tion of either 4-aminoquinolones (eq 43) or 4-aminoquinolines When condensed with �-dicarbonyl compounds, other
(eq 44) in fair (21 34%) to modest yields (59 79%).69 �-enaminonitriles based on the pyrazole nucleus afford
Avoid Skin Contact with All Reagents
8 TIN(IV) CHLORIDE
pyrazolo[3,4-b] pyridines in low (20%, eq 47) to modest (46 60%, Cyanohydrins also react with �-dicarbonyl compounds in the
eq 48) yields.71 presence of SnCl4 to afford substituted 4-amino-2,5-dihydro-2-
furanones (eqs 52 and 53).73
S
CN NH2
S
CO2R2
SnCl4
H2N COCH3
CN
R SnCl4
N
NH2 CH2(CO2R2 )2 N
(52)
N
R2
N
CH3COCH2CO2CH3
N O
OH
O
O
H R
Ph Ph R2
(47)
50-60%
S
CN
SnCl4 H2N CO2R2 2
CN
CH3COCH2CO2CH3 SnCl4
N R
NH2
R2
N
(53)
CH2(CO2R2 2 )2 O
OH
O
R
R2
Ph
60-80%
NH2
S
CO2CH3
Reactions of protected �-D-ribofuranosyl ketoesters (prepared
N
(48)
from �-D-ribofuranosyl cyanide) with alkyl cyanoformates pro-
N
N CH3
moted by tin(IV) chloride afford high yields of enamino ke-
Ph
toester intermediates. Reaction with either acetamidine or ben-
Unsaturated nitriles, e.g., acrylonitrile, readily react with zylhydrazine leads to the formation of pyrazole or pyrimidine
methyl acetoacetate in the presence of SnCl4 in a one-pot reac- C-nucleosides with no anomerization.74 A related series of sub-
tion leading to enamino ketoesters (eq 49), or substituted pyridine stituted pyrazole C-nucleosides can be approached by the reaction
derivatives (eqs 50 and 51) depending on the stoichiometry, sol- of the same ribofuanosyl cyanide with methyl acetoacetate.75
vent, and temperatures.72
Glycosylations. SnCl4 promoted glycosylations take advan-
SnCl4
CN
tage of stable, readily available protected or partially protected
O O
(3 equiv)
(1.5 equiv)
carbohydrates. Treatment of 1-O-acetyl-2,3,5-tri-O-benzoyl-�-D-
1,2 dichloroethane
O ribofuranose or peracetylated �-D-glucose with SnCl4 and an
rt
alcohol in dichloromethane affords high yields of the desired
glycosides with high anomeric purity (eqs 54 and 55).
O
BzO
OAc BzO
OR
O O
O
O
1. SnCl4
(49)
(54)
2. ROH
H2N
OBz OBz
OBz OBz
SnCl4
CN
O O
OAc
OAc
(0.4 equiv) (0.9 equiv)
OOAc 1. SnCl4
1,2-dichloroethane OOR
O
OAc
reflux (55)
OAc
2. ROH
O
OAc
OAc OAc
OAc
O
(50)
Participating groups on O-2 (e.g., acetyl or benzoyl) lead to a
HO N
preference for 1,2-trans glycosides while nonparticipating groups
(e.g., benzyl) afford 1,2-cis glycosides preferentially.76 The order
O
of addition is important for high anomeric selectivity when partic-
SnCl4 ipating O-2 groups are present. In a typical reaction the glycosyl
CN
O O
ć%
(0.9 equiv) donor and SnCl4 are combined at 0 C followed by the slow ad-
(0.4 equiv)
dition of the appropriate glycosyl acceptor. Several groups have
O toluene, 100 �C
noted that combining the glycosyl acceptor and donor in solution
O followed by addition of SnCl4 leads to mixtures of the anomeric
glycosides.77-80
O
SnCl4 mediated glycosylation enabled the coupling of a
(51)
lactone-based glycosyl acceptor to a peracetylated donor, thereby
N
affording entry to disaccharides with a furanose at the reducing
O O
end (eq 56).81,82
A list of General Abbreviations appears on the front Endpapers
TIN(IV) CHLORIDE 9
OAc
OAc
OMPM
OOAc SnCl4
O
O HO
OAc
OBz O + OAc
SPh
SnCl4-AgClO4
BzO
OAc PhIO, ether, -20 �C
OAc OBz
OBz
N3
OH
O
OAc
OBz O
O
BzO
OBz
OAc (58)
OAc
OMPM
(56)
O
OBz
OO
N3
OAc
OAc
OAc
A few coupling reactions have been noted in which the unpro-
tected nitrogen heterocycles are used directly.110-113,115 In cases
Attempts to use Koenigs-Knorr conditions to accomplish this
where several nucleophilic nitrogens are present, mixtures of re-
coupling afforded significant amounts of the ortho ester, a com-
gioisomers (about the nitrogen base ring) occur.96,97,102,107 The
mon side reaction under Koenigs-Knorr conditions. SnCl4 gly-
preferred glycosidation occurs on the endocyclic nitrogens. An ex-
cosylations have also been used to attach aglycons for enzyme
ception was found when 2-aminoimidazole (as its sulfate salt) was
kinetic studies (e.g., p-nitrophenol).83 Couplings to a wide range
coupled with 1-O-acetyl-2,3,5-tri-O-benzoyl-�-D-ribofuranose in
of carbohydrate acceptor alcohols have been conducted with the
the presence of SnCl4 and Hg(CN)2 wherein the unexpected gly-
successful formation of a diverse set of linkages types.82,83 N-
cosidation of the exocyclic 2-amino group occurred (eq 61).115
Acetylglucosamine has also been employed as a glycosyl acceptor
leading to the synthesis of important disaccharides (eq 57).84,85
TMS
Bz
OBz
OAc
N
O
SnCl4
O
SnCl4 OOAc
OBz
OBz N
CH2ClCH2Cl
N
OBz
+
OAc
+
60-70 �C
OBn BzO
N
OBz N
OH
OAc
NHAc
OAc
OBz
TMS
OBz
Bz TMS
O
N
OBz
N
OBn
N
(57)
O
NHAc
O
N
OBz N
(59)
AcO
O
BzO
OBz
OAc
OBz
OAc
OAc
Further work86-88 has led to SnCl4 promoted couplings with
69%
TMS-protected acceptors affording ą-glycosides. The coupling
of 3�-cholestanyl trimethylsilyl ether to glucose was studied in
regard to the Lewis acid. GaCl3 and SnCl4 were found to be Reactions involving additions of nitrogen bases to glycals
the most effective Lewis acids screened in the presence of 20 have also been reported.108,109 Anhydro-carbohydrates have
mole % AgClO4. In addition the effects of solvents were also also been reported to function as glycosyl donors towards
studied with diethyl ether providing the highest yields and best silylated acceptors.105 Internal C-glycosylations are possible
stereoselectivity.87,88 The combined catalyst system has been used when activated 3-methoxybenzyl protecting groups are used.
for the effective synthesis of isomalto-oligosaccharides.89,90 A When methyl 2,3,4-tri-O-(3-methoxybenzyl)-�-D-ribofuranoside
unique glycosidation involving a 2-deoxy-azido-thioglycoside/ was treated with SnCl4, instead of the simple internal Friedel-
iodosobenzene/SnCl4-AgClO4 system was used to prepare pre- Crafts product, a double internal cyclization occurred leading to
3
cursors to H-labeled lipid A (eq 58).91 an 88% yield of a tetrahydro-[2]benzopyrano[3,4-d]benzoxepin
Glycosidation reactions involving nitrogen bases, yielding (eq 62).116 The final product arises from sequential alkylations of
nucleosides, have also been investigated. Generally the ni- the O-2 and O-3 methoxybenzyl protecting groups.
trogen bases are converted into a silylated derivative before Substituted thiophenes have also been used as glycosyl accep-
coupling.92-111 Glycosyl donors can be either fully pro- tors resulting in the synthesis of purine-like C-nucleosides (eq
tected sugars92-98,100,102-104,107,111-113 [e.g., 1,2,3,4,6-penta- 63).117
O-acetyl �-D-glucose92 (eq 59) or glycosyl halides (eq C-Glycosylation reactions of 2-deoxy-4-thioribofuranosides
60)99,101,106,114]. Reaction yields using 1-O-acetoxy donors were (TRib) with silylated glycosyl acceptors give high yields of the
significantly better than those obtained by the use of glycosyl C-glycosides (65 89%) with a predominance of the ą-isomer (eq
halides. 64, Table 1).118
Avoid Skin Contact with All Reagents
10 TIN(IV) CHLORIDE
BzO
CH3 OAc COOCH3 SnCl4, (CH2Cl)2
OTMS
O
OP + S
reflux
N
SnCl4
Br
O N
NHCHO
+
CH2ClCH2Cl
OBz OBz
N
N
OP OP
BzO
TMS
O
P= 4-nitrobenzoyl
O
CH3
N
+
NHCHO
N
N
CH3 OBz OBz
NH
S
OP OP
NH
+ (60)
N
N
N COOCH3
O 10%
O
O
COOCH3
OP OP
OP OP
S
BzO
O
NHCHO
(63)
OBz OBz
50%
NH2
BzO
OAc
SnCl4
O
+ HN N
silylated
Hg(CN)2
AcO
nucleophile (Nu)
S
OEt
OBz OBz
SnCl2, CH3CN
OTBDMS
HN N
AcO
S
Nu
(64)
BzO NH (61)
O
OTBDMS
OBz OBz
Table 1
Nucleophile Product Yield (%) ą/�
OTMS O
TRib 65 1.1:1
PO
OMe
O
SnCl4
OP OP
O
TMSO
79 4.4:1
P = 3-methoxybenzyl
Ph Ph TRib
PO
O
SiMe3
TRib
84 100:0
H
SnCl4
PO
H
O
TRib
OMe
69 100:0
expected product SiMe3 CH3
OMe
OP
O
H
H
The use of silver trifluoroacetate-SnCl4 affords high yields of
(62)
aryl C-glycosidation products.119 When treated with a second
H
O
equivalent of glycosyl donor in the presence of SnCl4, a double
OH OMe
aryl C-glycosylation product can also be achieved in high yield
88%
(eq 65).120
A list of General Abbreviations appears on the front Endpapers
TIN(IV) CHLORIDE 11
OAc
chlorinated side product (eq 67). Reactions performed in either
OAc
ć%
MeO
toluene or dichloromethane at -97 C gave the best reaction re-
O SnCl4, AgOTFA
+
sults. Other reactions involving BINOL as the chiral auxiliary
AcO CH2Cl2
OAc
OMe
in SnCl4-mediated alkene cyclizations have led to the synthe-
OAc
sis of (S)-cembrene,122 (-)-ambrox and ( + )-podocarpa-8,11,13-
triene.123
OAc OAc
O
OAc
CH3
AcO
OAc
MeO
OAc
OAc
O
SnCl4, AgOTFA
OMe
AcO
CH2Cl2
SnCl4
OAc O
6-12 h
OR
H3C CH3
AcO
OAc
OAc
MeO
OAc
O
O
OMe
AcO
OAc
AcO
+ (67)
OAc
(65)
94% (second addition)
Cl
The spirosuccinimide compound (18), a mimic of the herbicide
( + )-hydantocin, owes its synthesis to the allylation of an easily
prepared protected D-psicofuranose in the presence of SnCl4 (eq
66).121 Attempted use of other Lewis acids (TMSOTf, BF3�OEt2, Diels Alder Reactions. Tin(IV) chloride has been shown to
TrClO4, and TiCl4) in this condensation resulted in the recovery be useful as a catalyst in the cyclization of 2-oxo-alkanoates with
of starting materials. simple alkenes (eq 68).124
TMS
BnO
O R1
O
SnCl4
R3 R2
O
SnCl4
CH2Cl2
+
0 �C, CH2Cl2
O O
MeO2C
O
R1 R2
R3
O
HO
BnO
O
O
(68)
NH
OH
(66)
O
MeO2C
OH OH
O O O
18
These cyclizations, which did not take place under conditions
83%
of high temperature or high pressure alone, required the presence
of SnCl4. The additions with cis- and trans-3-hexenes both took
+
place with retention of configuration (eq 69).
BnO
OH
O
Ph
O O
E-3-hexene
SnCl4, CH2Cl2
R O
0 �C, 8 h
4%
Ph
38%
Alkene Cyclizations. The asymmetric synthesis of (R)-limo- (69)
nene has been explored using Lewis acid catalysis in combination
R
O
with a chiral leaving group (BINOL).122 O-Neryl-BINOL ethers
Ph
undergoes cyclization with detachment of the chiral auxiliary in
Z-3-hexene
the presence of SnCl4 (eq 67).
SnCl4, CH2Cl2
Choice of the R group in the BINOL auxiliary influences the
R O
0 �C, 8 h
course of the reaction with small groups (H, Me, i-Pr) and to-
10%
sylate affording (S)-limonene in modest yields. Changing R to
the benzoate or p-trifluoromethylbenzoate groups caused pref-
erential cyclization to the (R)-isomer. While enantiomeric ex- Switching the 2-Ą component from simple alkenes to styrene
cess levels tended to be good, the reaction usually included the afforded mixtures of products (eq 70).125
Avoid Skin Contact with All Reagents
12 TIN(IV) CHLORIDE
OP
Ph
H
styrene, SnCl4
H3C
N
O
CH2Cl2, 0 �C, 3 h
MeO2C
CH2 94% Ar OMe
O
12 CO2Me
N
Ph Ph
OP
(73)
Ar
O
(70)
+
CH3
MeO2C MeO2C Ph
Ph
P = Bn; 80% (cis)
P = TBDMS; 49% (trans)
trans/cis =73:27
ć%
Treatment of 1H-indol-3-ylmethanol with SnCl4 at -78 C af-
Kinetic studies with deuterium labeled styrene revealed the re-
fords the stable indolyl cation 19, which then undergoes addition
action to proceed by both concerted and ionic (stepwise) mecha-
of alkenes to yield cyclopenta[b]indoles with a good stereoselec-
nisms, with the initial products undergoing further isomerizations
tivity (eq 74).129 This is in contrast to the formation of diindol-3-
under the reaction conditions, but not by a retro-Diels-Alder mech-
ylmethane that is typically observed on generation of 1H-indol-
anism.
3-ylmethanol with protic acids.
[3 + 2] Cycloaddtions. Highly substituted tetrahydrofurans
OH
have been prepared by the SnCl4-mediated [3 + 2] cyclization of
4 equiv SnCl4
ą-ketoesters with allylsilanes.126,127 The order of addition plays
an important role in the outcome of the reaction. Tin(IV) chloride
CH2Cl2, -78 �C
N
added as a dilute solution in dichloromethane to the ą-ketoester
R
ć%
and allylsilane, in dichloromethane at -78 C, yielded a 50 85%
R = H, Me
of the substituted tetrahydrofurans (eq 71). Other addition se-
quences led to predominantly homoallyl alcohol formation.
Ph
CH3
Other Lewis acids tested, including TiCl4, AlCl3,
CH3
SnCl2, Sn(OTf)2, BF3�Et2O, or ZnCl2, afforded no [3 + 2]
(74)
Ph
E:Z = 9:1
addition products. Tetrahydrofuran formation is favored with
N+ N
TBDMS-based allylsilanes or by the presence alkyl substituents
R
R
19
ą- to the silyl group owing to stabilization of an intermediate
55%
�-carbocation, which in turn leads to cyclization (eq 72).
O
Ene Reactions. Chiral diazodicarboxylates have been demon-
R
OEt
strated to undergo an azo-ene reactions with alkenes mediated by
Ph
SnCl4, offering an easy entry into the formation of chiral allylic
O
OH
amines. Couplings of di-(-)-(1R, 2S)-2-phenyl-1-cyclohexyl-
Ph
O
EtO
+ (71) diazene dicarboxylate (DPCDD) with selected alkenes (e.g.,
Ph
ć%
cyclohexene) were carried out in dichloromethane at -60 Cin
CO2Et
O
R
the presence of SnCl4 (eq 75).130
O
Alcohol Yield (%)
R THF Yield (%) *AO
SnCl4, -60 �C
+
N N
SiMe3
50 41 CH2Cl2
OA*
SiPhMe2
54
46
O
TBDMS 85
6
O
Ph
CH3
*AO
O
O
N N (75)
Ph
R O
CH3
A* =
EtO
OEt H OA*
(72)
Ph SnCl4
O
O
O
R
Note: Chiral auxilary is attsched via ester link.
82%
R = SiPhMe2
Less bulky alkenes led to the formation of higher ratios of di-
Unlike the previously described addition of simple aldehydes astereomers. The adducts were cleaved with lithium/ammonia fol-
with oxazole (eq 32), protected (S)-2-hydroxypropanals add to lowed by hydrolysis of the resulting carbamate to yield the ally-
oxazole 12 to afford good yields of trans (P = TBDMS) or cis lamines.
addition products (P = Bn). Other Lewis acids screened, includ-
ing (BINOL)AlMe, TiCl4, BF3�Et2O, Et2AlCl, and AlMe3, gave Baeyer-Villiger. The combination of bis-(trimethylsilyl)
mixtures of isomers (eq 73).128 perxoide/Lewis acid/diamine offers promise in the effort to
A list of General Abbreviations appears on the front Endpapers
TIN(IV) CHLORIDE 13
achieve enantioselective BV reactions.131 Galium(III) chloride 15. Scavo, F.; Helquist, P., Tetrahedron Lett. 1985, 26, 2603.
and tin(IV) chloride were determined to be the most effective 16. Deng, M. Z.; Caubere, P.; Senet, J. P.; Lecolier, S., Tetrahedron 1988,
44, 6079.
Lewis acid catalysts, with SnCl4 being cheaper and offering bet-
ter yields. Reduction of lactone ring opening and other side re- 17. Gras, J. L.; Galledou, B. S., Bull. Soc. chem. Fr. Part 2 1982, 89.
18. Martin, O. R.; Rao, S. P.; Kurz, K. G.; El-Shenawy, H. A., J. Am. Chem.
actions was accomplished by the addition of complexing ligands
Soc. 1988, 110, 8698.
reducing Lewis acidity of the catalyst. The most effective ligand
19. Showalter, H. D. H.; Putt, S. R., Tetrahedron Lett. 1981, 22, 3155.
was found to be trans-1,2-diaminohexane(DA). Optimum reac-
20. Wagner, D.; Verheyden, J. P. H.; Moffat, J. G., J. Org. Chem. 1974, 39,
tion conditions are depicted in eq 76.
24.
O
21. Hori, H.; Nishida, Y.; Ohrui, H.; Meguro, H., J. Org. Chem. 1989, 54,
4 � Molecular sieves
CH3 25 mole % (1:1 SnCl4/DA)
1346.
22. Hopkins, M. H.; Overman, L. E., J. Am. Chem. Soc. 1987, 109, 4748.
2 equiv Me3Si-O-O-SiMe3
23. Overman, L. E.; Kakimoto, M. E.; Okazaki, M. E.; Meier, G. P., J. Am.
CH2Cl2, 5 �C
Chem. Soc. 1983, 105, 6622.
91%
24. Herrington, P. M.; Hopkins, M. H.; Mishra, P.; Brown, M. J.; Overman,
L. E., J. Org. Chem. 1987, 52, 3711.
O
O
25. Review of ą-alkylations to carbonyl compounds: Reetz, M. T., Angew.
CH3
O Chem., Int. Ed. Engl. 1982, 21, 96.
O
+ (76)
26. (a) Review of asymmetric alkene cyclization: Bartlett, P. A. Asymmetric
CH3
Synthesis; Morrison, J. D., Ed.; Academic:New York, 1984; Vol. 3, Part
B, p 341. (b) Review of thermal cycloadditions: Fallis, A. G.; Lu, Y.-
31:1
F. Advances in Cycloaddition; Curran, D. P., Ed.; JAI:Greenwich, CT,
1993; Vol. 3, p 1.
27. (a) Overman, L. E.; Blumenkopf, T. A.; Castaneda, A.; Thompson, A.
Related Reagents. Tin(IV) Chloride Zinc Chloride.
S., J. Am. Chem. Soc. 1986, 108, 3516. (b) Overman, L. E.; Castaneda,
A.; Blumenkopf, T. A., J. Am. Chem. Soc. 1986, 108, 1303.
28. Demailly, G.; Solladie, G., J. Org. Chem. 1981, 46, 3102.
1. (a) Shambayati, S.; Crowe, W. E.; Schreiber, S. L., Angew. Chem.,
29. Murphy, W. S.; Waltanansin, S., J. Chem. Soc., Perkin Trans. 1 1982,
Int. Ed. Engl. 1990, 29, 256. (b) Reetz, M. T. In Selectivities in Lewis
1029.
Acid Promoted Reactions; Schinzer, D., Ed.; Kluwer:Dordrecht, 1989;
30. (a) Kamigaito, M.; Madea, Y.; Sawamota, M.; Higashimura, T.,
p 107. (c) Denmark, S. E.; Almstead, N. G., J. Am. Chem. Soc. 1993,
Macromolecules 1993, 26, 1643. (b) Takahashi, T.; Yokozawa, T.;
115, 3133.
Endo, T., Makromol. Chem. 1991, 192, 1207. (c) Ran, R. C.; Mao,
2. Davies, G. A.; Smith, P. J. In Comprehensive Organometallic
G. P. J., Macromol. Sci. Chem. 1990, A27, 125. (d) Kurita, K.;
Chemistry; Wilkinson, G.; Stone, F. G. A.; Abel, E. W., Eds.;
Inoue, S.; Yamamura, K.; Yoshino, H.; Ishii, S.; Nishimura, S. I.,
Pergamon:New York, 1982; Vol. 2, p 519.
Macromolecules 1992, 25, 3791. (e) Yokozawa, T.; Hayashi, R.; Endo,
T., Macromolecules 1993, 26, 3313.
3. Naruta, Y.; Nishigaichi, Y.; Maruyama, K., Tetrahedron 1989, 45, 1067.
31. (a) Tanaka, H.; Kato, H.; Sakai, I.; Sato, T.; Ota, T., Makromol. Chem.
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