TIN(IV) CHLORIDE ZINC CHLORIDE 1
conjugated dimethyl acetals provide dipropargyl derivatives as
Tin(IV) Chloride Zinc Chloride1
side products. Ethynylation of aldehydes is accomplished by form-
ing intermediate hemiacetal-like compounds from aldehydes and
SnCl4 ZnCl2
alkoxytrimethylsilanes in the presence of the Lewis acid blend.
These intermediates then undergo reaction with 1-trimethylsilyl-
(SnCl4)
1-alkynes to form the desired secondary propargylic ethers (eq 2).
[7646-78-8] Cl4Sn (MW 260.51)
10% SnCl4 ZnCl2
InChI = 1/4ClH.Sn/h4*1H;/q;;;;+4/p-4/f4Cl.Sn/h4*1h;/q4*-1;m
OR2
CH2Cl2, rt
InChIKey = HPGGPRDJHPYFRM-LUCXXLOKCB R1 + R3 TMS
13 85%
OR2
(1)
(ZnCl2)
[7646-85-7] Cl2Zn (MW 136.29)
R2O
InChI = 1/2ClH.Zn/h2*1H;/q;;+2/p-2/f2Cl.Zn/h2*1h;/q2*-1;m
R3 (1)
R1
InChIKey = JIAARYAFYJHUJI-ATOKYBHQCC
1. cat. SnCl4 ZnCl2
(catalyst for bond formation between silyl nucleophiles and
2. R2OTMS
O
R2O
carbonyl groups or enones1)
3. (1)
R3 (2)
ć% ć%
R1 H
0 78%
Physical Data: SnCl4: mp-33 C; bp 114.1 C; d 2.226 g cm-3;
R1
ć% ć%
ZnCl2: mp ca. 290 C; bp 732 C.
Solubility: both reagents react violently with water. SnCl4: sol
cold H2O; dec hot H2O; sol alcohol, ether, CCl4, benzene, Allylation of Secondary Propargylic Ethers and
ć%
toluene, acetone. ZnCl2: sol H2O (432 g/100 g at 25 C, 614 Aldehydes.1 Propargylic ethers are allylated by Allyltrimethyl-
ć%
g/100 g at 100 C); 2% HCl (4 g/1 mL); alcohol (1 g/1.3 mL); silane in the presence of the SnCl4 ZnCl2 blend (eq 3). Thus
glycerol (1 g/2 mL); freely sol acetone. acetals can be transformed to 1,5-enynes in one pot with
Form Supplied in: blend not commercially available. Anhydrous sequential nucleophilic additions. The blend also catalyzes
SnCl4: colorless liquid; 1 M soln CH2Cl2 or heptane; widely the allylation of aldehydes by allyltrimethylsilane, yielding
available. Anhydrous ZnCl2: white, odorless granules, lumps, homoallylic alcohols in good yields (61 74%).
or rods; 1 M soln in Et2O, 0.5 M soln in THF; widely available.
TMS
Purification: SnCl4: heat to reflux with mercury or P2O5 for sev-
MeO
cat. SnCl4 ZnCl2
Ph
eral hours, then distil under reduced nitrogen pressure into re-
Ph (3)
56%
ceiver with P2O5. Redistil. Typical impurities: hydrates. ZnCl2:
Ph
heat to reflux in dioxane (100 g/800 mL) with zinc dust (10 g),
Ph
filter hot, and cool to precipitate ZnCl2. Crystallize from diox-
ane. Impurities: H2O, zinc oxychloride.
Handling, Storage, and Precautions: both reagents are hygro- Aldol and Michael Reactions.1 The SnCl4 ZnCl2 blend is
an effective catalyst in the aldol reaction of silyl enol ethers with
scopic and should be stored in a glove box or over P2O5 to
aldehydes (eq 4), acetals (eq 5), or ketones. The product anti/syn
minimize exposure to moisture. Containers should be flushed
with N2 or Ar and tightly sealed. Perform all manipulations un- ratios are variable (32:69 to 89:11). The blend also catalyzes the
Michael addition of silyl enol ethers with Ä…,²-unsaturated ketones
der N2 or Ar. Solvating SnCl4 with H2O is highly exothermic.
Use in a fume hood. (eq 6), yielding alkylation products (84 100%) with anti selectiv-
ity (anti/syn = 55:45 to 87:23)
O OH
OTMS O
SnCl4 ZnCl2
Introduction. The Tin(IV) Chloride Zinc Chloride blend1
(4)
+
Ph Ph
Ph H 99%
is one of many Lewis acid blends, such as Sn(OTf)2 Bu3SnF,2 Ph
SnCl4 Sn(OTf)2,3 SbCl5 Sn(OTf)2,4 TMSCl SnCl2,5
O OMe
TrCl SnCl2 (Tr = trityl),6 SnO TMSOTf,7 and GaCl3 AgClO4,8
OTMS
OMe
SnCl4 ZnCl2
which are effective catalysts in carbon carbon bond forming (5)
+
Ph
Ph Ph
99%
+
reactions. The active catalyst is believed to be ZnCl SnCl5- Ph OMe
which is formed prior to the addition of organic reactants. Single
O
Lewis acids (SnCl4, TiCl4, etc.) promote these reactions, but do
OTMS O
SnCl4 ZnCl2
not catalyze them.9
+ (6)
Ph 87% Ph O
Ethynylation of Acetals and Aldehydes.1 The SnCl4 ZnCl2
blend is the most useful catalyst (10 mol %) for the preparation of
Related Reagents. Tin(IV) Chloride; Zinc Chloride.
secondary propargylic ethers from 1-trimethylsilyl-1-alkynes and
acetals (eq 1).1 Conventional promoters such as TrCl SnCl2 and
TMSCl SnCl2 are not effective, and SnII SnIV, SnII TiIV, and
ZnII TiIV blends provide lower yields. Moderate yields (29 53%)
1. (a) Hayashi, M.; Inubushi, A.; Mukaiyama, T., Bull. Chem. Soc. Jpn. 1988,
are obtained for acetals with large alkoxy groups (R2); however,
61, 4037. (b) Hayashi, M.; Inubushi, A.; Mukaiyama, T., Chem. Lett. 1987,
cyclic acetals, such as 1,3-dioxolane, do not react. Aromatic and 1975.
Avoid Skin Contact with All Reagents
2 TIN(IV) CHLORIDE ZINC CHLORIDE
2. (a) Mukaiyama, T.; Uchiro, H.; Kobayashi, S., Chem. Lett. 1989, 1001. 7. Mukaiyama, T.; Uchiro, H.; Kobayashi, S., Chem. Lett. 1990, 1147.
(b) Kobayashi, S.; Mukaiyama, T., Chem. Lett. 1989, 297. (c) Kobayashi,
8. Mukaiyama, T.; Ohno, T.; Nishimura, T.; Suda, S.; Kobayashi, S., Chem.
S.; Uchiro, H.; Fujishita, Y.; Shiina, I.; Mukaiyama, T., J. Am. Chem. Soc.
Lett. 1991, 1059.
1991, 113, 4247.
9. (a) Mukaiyama, T.; Narasaka, K.; Banno, K., Chem. Lett. 1973, 1011. (b)
3. Mukaiyama, T.; Shimpuku, T.; Takashima, T.; Kobayashi, S., Chem. Lett.
Mukaiyama, T., Angew. Chem., Int. Ed. Engl. 1977, 16, 817. (c) Narasaka,
1989, 145.
K.; Soai, K.; Aikawa, Y.; Mukaiyama, T., Bull. Chem. Soc. Jpn. 1976, 49,
4. Kobayashi, S.; Tamura, M.; Mukaiyama, T., Chem. Lett. 1988, 91. 779.
5. (a) Iwasawa, N.; Mukaiyama, T., Chem. Lett. 1987, 463. (b) Mukaiyama,
T.; Wariishi, K.; Saito, Y.; Hayashi, M.; Kobayashi, S., Chem. Lett. 1988,
Stephen Castellino
1101.
Rhône-Poulenc Ag. Co., Research Triangle Park, NC, USA
6. (a) Mukaiyama, T.; Kobayashi, S.; Tamura, M.; Sagawa, Y., Chem. Lett.
David E. Volk
1987, 491. (b) Mukaiyama, T.; Sugumi, H.; Uchiro, H.; Kobayashi, S.,
North Dakota State University, Fargo, ND, USA
Chem. Lett. 1988, 1291.
A list of General Abbreviations appears on the front Endpapers