HYPOPHOSPHOROUS ACID 1
O
H
Hypophosphorous Acid1
P
dioxane, (t-BuO)2 OH
+ H3PO2 (2)
70%
H3PO2
[6303-21-5] H3O2P (MW 66.00)
Hydroxyalkylphosphinic Acids. HPA reacts with aldehydes,
InChI = 1/H3O2P/c1-3-2/h3H2,(H,1,2)/f/h1H
ketones, and 1,2-ketones to provide 1-hydroxyalkylphosphinic
InChIKey = ACVYVLVWPXVTIT-OKIMJQNECY
acids (eq 3).1 When carbonyl compounds are used in excess, bis(1-
(tautomer)
hydroxyalkyl)phosphinic acids are formed.
[14332-09-3]
O OH
InChI = 1/H3O2P/c1-3-2/h1-3H
+ H3PO2 O (3)
InChIKey = XRBCRPZXSCBRTK-UHFFFAOYAT
Cl3C H Cl3C P
65%
H
OH
(reduction of aromatic diazonium salts,1,2 nitro compounds,3 and
pyrrole derivatives;4 synthesis of organic derivatives of hypophos-
phorous acid;1,5,6 generation of selenols7)
1,2-Alkadienylphosphinic Acids. Reactions of HPA with
Alternate Name: HPA. alkynic alcohols are accompanied by alkyne allene rearrange-
ć% ć%
Physical Data: mp 26.5 C; decomposes at 140 C; d 1.493 ment and lead to 1,2-alkadienylphosphinic acids (eq 4).15
ć%
gcm-3 (19 C); pKa 1.1.
O H
Solubility: soluble in water, alcohol, ether, dioxane.
R1 R1 P OH
benzene, reflux
Form Supplied in: widely available as 50% aqueous solutions
+ H3PO2 (4)
R2 R3 "
96%
(d 1.274 g mL-1).
HO R2 R3
Preparative Methods: the anhydrous acid is prepared from the
R1 = R2 = H; R3 = CH2OH
commercial solution or from inorganic salts.1,8
Handling, Storage, and Precaution: decomposes upon heating
ć%
above 140 C into H3PO4 and poisonous, spontaneously flamm-
Aminoalkylphosphinic Acids. HPA reacts with azomethines
able PH3. Slowly decomposes at rt. Air sensitive. Use in a fume
under mild conditions, providing good yields of 1-(alkylamino)
hood.
alkylphosphinic acids.1 Synthetic possibilities of this reaction
have been extended by replacing the azomethines with a mix-
ture of aldehyde or ketone and amine or hydrazine.6,16 Thus re-
action of HPA with equimolar amounts of formaldehyde and sec-
ondary amines at rt in aqueous solution gives the corresponding
Original Commentary
dialkylaminophosphinic acids (eq 5). With an excess of amine
Vladimir V. Popik
and formaldehyde, bis(dialkylaminoalkyl)phosphinic acids are
St. Petersburg State University, St. Petersburg, Russia
formed.1,16
O Me O
Me
Reduction of Arenediazonium Compounds. Hypophospho- 20 �C
H
+ + H3PO2 (5)
NH N P
rous acid is widely accepted as the preferred reagent for the reduc-
H H Me OH
81%
Me
tion of diazonium salts.1,2,9 Copper(I) Oxide is a very effective
catalyst of this reaction9 (eq 1). Dediazonation with HPA can also
be used in Pschorr-type cyclizations.10
Alkyl Hypophosphites. A particularly easy preparation of
alkyl hypophosphites involves the reaction of crystalline HPA
with orthocarbonyl compounds (eq 6).5 Treatment of HPA with
Cl Cl
diazoalkanes also gives good yields of the desired esters.17 Reac-
H3PO2, Cu2O, CHCl3
tion of HPA with orthoformates in the presence of p-Toluenesul-
(1)
Cl N N+ Cl
fonic Acid leads to the formation of alkyl dialkoxymethylphos-
97%
BF4
phinates.18
O OR O
1 30 min
+ (6)
P P
H OH RO OR  ROH,  HCO2R H OR
H H
57%
Alkylphosphinic Acids. Radical addition of HPA or its alkali R = Et
salt to alkenes is initiated by organic peroxides and gives phos-
phinic acid derivatives in good yields (eq 2).1,6,11,12 The alkene
to HPA ratio controls the formation of alkyl- or dialkylphosphinic Reduction with Hypophosphorous Acid. Palladium on Car-
acid.1,11 Alkyl phosphinates also add to alkenes in the presence bon catalyzed reduction with HPA converts the nitro group of
of peroxides.1 Alkylphosphinic acids can be prepared from HPA arenes into an amino group,3 and quinones into hydroquinones.19
and alcohols,13 and alkenylphosphinic acids have been obtained HPA in combination with Hydrogen Iodide is used for reduction
from enol esters.14 and reductive alkylation of pyrrole derivatives.4
Avoid Skin Contact with All Reagents
2 HYPOPHOSPHOROUS ACID
Selenols. A commercial 50% solution of HPA is a convenient and oxidation to give pure ą-aminophosphonic acids (9) in high
reagent for generation of selenols from diselenides or selenic optical purity (eq 10).
acids.7
H H
H3PO2
R C NHCOMe R C PO2H2
CH3CO2H
NHCOMe NHCOMe
First Update
5 6
Andrew G. Wright, Tanweer A. Khan & John A. Murphy
R = X-C6H4
University of Strathclyde, Glasgow, UK
(X = H, Cl, Me, OMe, NO2, Br)
Non-radical Uses of Hypophosphorous Acid (HPA).
H
1. Hydrochloric acid
ą �-Unsaturated Amides. Cates and Li20
Addition of HPA to ą �
ą,�
R C PO2H2
(9)
2. Propylene
reported the first synthesis of a phosphinic acid containing an
NH2
oxide
amido group (1), using HPA in the addition to acrylamide (2)
(eq 7). Reaction between HPA and methacrylamide with ethanol as
7
31 72%
solvent gave only methacrylamide polymer as the product. Com-
pound 1 is the sole example of a phosphinic acid possessing an
Ph
amido side-chain.
NH
Ph
+ 
EtOH
NH3 H2PO2 RCHO OH
O O
R P
H
H3PO2 + 8
NH2 H2O2P NH2 (7) O
2 1, 73%
NH2
Br2 /H2O
(10)
R P (OH)2
Reaction of HPA Salts with Alkyl Halides. Devedjiev et
O
al.21 reported that alkali metal salts of HPA react with alkyl
9
halides through a variant of the Michaelis Bekker reaction. When
potassium hypophosphite was reacted with excess 3-chloro-1,2-
propanediol (3), 2,3-dihydroxypropylphosphinic acid (4) was
Synthesis of Oxazaphosphinanes. Cristau et al.25 reacted
formed (eq 8).
HPA with imine 10 to give phosphinic acid 11 which undergoes
intramolecular esterification to give oxazaphosphinane 12 in 55%
HO
+
P OK Cl OH yield (eq 11).
H
OH
3
OH
H
MeOH
reflux
+
HO POH (8) H3PO2
N
69%
OH
O
4
10
This has also been applied22 to the reaction with appropriate
halogenated polymers, e.g., PVC and polychloroprene rubber.
O
OH
OH
Direct Amidoalkylation of HPA. The synthesis of aminoben-
DCC/DMAP
P
zylphosphinic acids by the amidoalkylation of HPA using N,N - H
55%
arylidene bisamides has been reported by Tyka and H�gele.23 The
N
H
reaction of bisamides (5) with HPA and acetic acid gave interme-
diate 6 which, upon treatment with hydrochloric acid and propy-
11
lene oxide, gave product 7(eq 9). Only bisamides prepared from
aromatic aldehydes undergo these reactions.
O
O
ą
Synthesis of ą
ą-Aminophosphonic Acids Using HPA. Hamil-
P H
ton and co-workers24 developed a convenient route to opti-
(11)
cally pure ą-aminophosphonic acids by reacting the HPA salts
N
H
of R-(+) or S-(-) N-ą-methylbenzylamine (8) with a vari-
ety of aldehydes in refluxing ethanol to form intermediate
12
ą-aminophosphinic acids followed by simultaneous deprotection
A list of General Abbreviations appears on the front Endpapers
HYPOPHOSPHOROUS ACID 3
Preparation of Hypophosphite Esters. DeprŁle and tions and dehalogenations with HPA have been reported by Barton
Montchamp26 have synthesized hypophosphite esters using et al.31
alkoxysilanes. They found that anilinium hypophosphite (AHP,
H3PO2
X H
13) reacted with orthosilicates in a wide range of solvents (e.g.,
AIBN
benzene, cyclohexane, toluene, THF, dioxane, acetonitrile, DMF)
base
to give the corresponding hypophosphite esters (14) in excellent (14)
Dioxane
yields (eq 12).
reflux
17, X = O-C=S(SMe) 18, X= H, 100%
Si(OR)4
O
O 19, X = I 18, X = H, 100%
solvent
H H
20, X = Br 18, X = H, 95%
heat
RO P (12)
MO P
85 100%
H H
Jang32 subsequently reported that radical dehalogenation can
13, M = PhNH3 14
also be achieved in water, as opposed to toxic organic solvents.
The synthesis of enantiopure (R)-malates from (R,R)-tartrates via
cyclic thionocarbonates using a HPA/Et3N/AIBN system in diox-
HPA-iodine as a Novel Reducing System. Fry and co-workers
ć%
ane at 80 C has been reported by Jang and Song.33
developed a novel reducing system using HPA and a catalytic
amount of iodine in refluxing acetic acid.27 The reduction of diaryl
Synthesis of Monosubstituted Phosphinic Acids. DeprŁle and
ketones (15) to diaryl methylene derivatives (16) has been reported
Montchamp34 reported that phosphorus-centered radicals, gener-
in an excellent yield, and it was found that diaryl ketones reduce
ated by initiation with triethylborane and oxygen, can react with a
much more readily than aryl-alkyl ketones which, in turn, are
wide variety of alkenes to give monosubstituted phosphinic acids
reduced more rapidly than dialkyl ketones (eq 13).
(21) in good to excellent yields (eq 15). When the reaction was
attempted with electron-deficient alkenes, the yields were greatly
O
H3PO2, I2
reduced. These radical reactions are conducted at room temper-
CH3COOH
reflux
ature in an open flask without the use of potentially explosive
(13)
98% peroxide initiators.
O O
Et3B/O2
15 16
H
H
MeOH
R
MO P MO P
(15)
70 98%
R
H
Subsequently, Fry applied this reducing system to the reduction
21
of benzhydrols28 and of diarylethenes29 to diarylethane deriva-
tives. Acetic acid has proven to be the solvent of choice for this M = Na, PhNH3
system. Reduction of benzhydrols was slow or negligible in chlo-
roform or benzene and conversion to the methyl ether was ob-
served using methanol. The issue of selective reduction has also
Intramolecular Carbon Carbon Bond Formation.
been addressed and it was found that when an equimolar mixture
Hypophosphite-mediated carbon-carbon bond formation was
of benzophenone and 3,4-dimethylbenzhydrol was reacted under
developed in the 1990 s to avoid the problems associated with tri-
the standard reducing conditions, the alcohol was converted com-
butyltin hydride.35-40 The reaction by-products are water-soluble
pletely to 3,4-dimethyldiphenylmethane without any detectable
and easily separated, and HPA is considerably more econom-
reduction of benzophenone to diphenylmethane.28
ical than either tributyltin hydride or tris(trimethylsilyl)silane
(TTMSS).
Radical Uses of HPA.
Radical Addition to Alkynes. The first published example of
Radical Deoxygenation and Dehalogenation Using HPA.
carbon-carbon bond formation using HPA and its salts was car-
Barton et al.30 reported that HPA can be used for the defunc-
ried out35 by Calderon and co-workers. Stoodley and co-workers36
tionalization of several functional groups. Radical chain deoxy-
followed this with the construction of near-stereopure quaternary
genations can be carried out using phosphorus-centered radicals
carbon stereogenic centers in molecules such as 22 starting from
generated from hypophosphorous acid or its salts with initia-
alkyl bromides such as 23. These cyclizations, which were me-
tion by 2,2 -azobis(2-methylpropionitrile) (AIBN). When treated
diated by N-ethylpiperidine hypophosphite (EPHP) and initiated
with HPA and a tertiary nitrogen base (e.g., triethylamine or
by AIBN in refluxing toluene, gave the cyclized product in high
N-ethylpiperidine) in boiling dioxane, alcohol thiocarbonyl
yield (eq 16).
derivatives (17) were deoxygenated to give 18 in excellent yield.
The tertiary nitrogen base protects the thiocarbonate moiety as
O Me
EPHP
well as any acid labile protecting groups from acidic hydrolysis
AIBN
Me
Br
during the reaction (eq 14). This method is applicable to thio-
O
O (16)
Toluene
Me
carbonyl derivatives of primary, secondary, and tertiary alcohols.
Me
reflux
H
Radical dehalogenation reactions have also been achieved using OR
OR 79%
O
this method with iodide 19 and bromide 20 similarly giving hydro-
22
23
carbon 18 in excellent yields (eq 14). Further radical deoxygena-
Avoid Skin Contact with All Reagents
4 HYPOPHOSPHOROUS ACID
Radical Addition to Alkenes. Carbon-carbon bond formation of 2,3-disubstituted indoles. Cyclization of o-alkenylthioanilide
has also been accomplished using HPA and its salts via addition precursor 31 proceeds smoothly to furnish the corresponding 2,3-
of carbon radicals to alkenes in a 5-exo-trig cyclization. The first disubstituted indole 32 in a good yield (eq 19).
example of this sort of carbon-carbon bond formation was reported
by Murphy and co-workers37 when they reacted aryl iodides (24)
with EPHP and AIBN in refluxing toluene to give the 5-exo-trig
H3PO2
OH
cyclized products (25) in moderate yields. Alkyl bromides (26) AIBN
Et3N
gave the cyclized products (27) in good to excellent yields (eq 17).
n-PrOH, "
NH
71%
EPHP (10 equiv)
O R
O
S
AIBN (0.4 equiv)
R2 2
5-exo-trig
R2 2 R2
I
OH
31
24
R2
R
N
25 (19)
H
R R2 R2 2 Yield (%)
32
H H H 64
Me H H 63
Me Me H 66
H Cyclohexyl 64
Fukuyama42 has applied this methodology in the total synthe-
sis of the Iboga alkaloid (ą)-catharanthine (33). Cyclization of
H
EPHP (10 equiv)
O O R O
O
the thioanilide precursor 34 gives indole 35 in 40 50% yield, a
AIBN (0.4 equiv)
R2 2
(17)
considerable improvement in the yield obtained (12 22%) for the
R2 2 R2 5-exo-trig
Br
same reaction using tributyltin hydride (eq 20). These conditions
H
are particularly effective for the construction of indoles bearing
26
R2
R
sterically demanding substituents in the 2-position.
27
R R2 R2 2 Yield (%)
H H H 85
AIBN
Me H H 94
AcO
Z
H3PO2
Me Me H 81
NEt3
H 76 S N
Cyclohexyl
1-Propanol
N
H
Murphy and co-workers38 have since applied this methodology
CO2Me
to the total synthesis of the phytotoxic metabolites epialboatrin
34
(28) and alboatrin (29), which were synthesized via 5-exo-trig
AcO
cyclization of bromochroman (30) to give 28 and 29, in a 6.7:1 Z
ratio and a yield of 77% (eq 18).
N
N
EPHP
H
Br AIBN
CO2Me
Benzene
35
77%
TBSO O O
N
(20)
30
N
H
CO2Me
H H
33
(18)
O O
HO O HO O
28 29
Radical Cyclization of Hydrophobic Substrates in Water.
Oshima39,40 has also shown that salts of HPA can be used to Kita et al.43 reported that a combination of water-soluble radi-
mediate radical cyclizations onto alkenes in aqueous ethanol using cal initiator 2,2 -azobis[2-(2-imidazolin-2-yl)propane] (VA-061),
triethylborane and oxygen as initiator. water-soluble chain carrier EPHP, and surfactant cetyltrimethyl-
ammonium bromide (CTAB) gave the optimum conditions for
Synthesis of Indoles Using HPA Fukuyama and co-workers41 carrying out radical cyclizations of hydrophobic substrates in
have used the HPA/AIBN/Et3N system to synthesize a variety water in an excellent yield (eq 21).
A list of General Abbreviations appears on the front Endpapers
HYPOPHOSPHOROUS ACID 5
I
4. (a) Gregorovich, B. V.; Liang, K. S. Y.; Glugston, D. M.; MacDonald, S.
F., Can. J. Chem. 1968, 46, 3291. (b) Khan, S. A.; Plieninger, H., Chem.
VA-061
Ber. 1975, 108, 2475. (c) Corbella, A.; Gariboldi, P.; Jommi, G.; Mauri,
EPHP
N
F., Chem. Ind. (London) 1969, 583.
CTAB
Ms
MeO 5. (a) Baudler, M., In Organic Phosphorus Compounds; Kosolapoff,
H2O, 80 �C
G. M.; Maier, L., Eds.; Wiley: New York, 1973, p 1. (b) Livantsov,
98%
M. V.; Prishchenko, A. A.; Lutsenko, I. F., J. Gen. Chem. USSR (Engl.
Transl.) 1985, 55, 2226.
6. Kleiner, H.-J., Methoden Org. Chem. (Houben-Weyl) 1982, E1, 271.
N
(21) 7. (a) Labar, D.; Krief, A.; Hevesi, L., Tetrahedron Lett. 1978, 41, 3967.
Ms
(b) Synthetic Methods of Organic Chemistry; Theiheimer, W., Ed.;
MeO
Karger: Basel, 1968; Vol. 22, p 19.
8. Handbook of Preparative Inorganic Chemistry; Brauer, G., Ed.;
Academic: New York, 1963, p 555.
Intermolecular Carbon Carbon Bond Formation. Jang and
9. Korzeniowski, S. H.; Blum, L.; Gokel, G. W., J. Org. Chem. 1977, 42,
co-workers44 have reported the first intermolecular radical carbon-
1469.
carbon bond formation by HPA or its salts. They studied the radical
10. Dattolo, G.; Cirrincione, G.; Almerico, A. M.; Aiello, E.; D Asdia, I., J.
addition of alkyl halides (36) to electron-poor alkenes (37) with
Heterocycl. Chem. 1986, 23, 1371.
triethylborane/oxygen as initiator and dioxane as solvent to give
11. Nifant ev, E. E.; Magdeeva, R. K.; Dolidze, A. V.; Ingorokva, X. X.;
addition product 38 in high yields (eq 22).
Samkharadze, L. O.; Vasyanina, L. K.; Bekker, A. R., J. Gen. Chem.
EPHP, Et3B USSR (Engl. Transl.) 1991, 83.
Dioxane, O2, rt
R 12. Broan, C. J.; Cole, E.; Jankowski, K. J.; Parker, D.; Pulukkody, K.; Boyce,
(22)
R X Y Y
B. A.; Beeley, N. R. A.; Millar, K.; Millican, A. T., Synthesis 1992, 63.
36 37 38
13. Devedjiev, I.; Ganev, V.; Stefanova, R.; Borisov, G., Phosphorus Sulfur
Silicon 1987, 31, 7.
RY Yield (%)
14. Holt, D. A.; Erb, J. M., Tetrahedron Lett. 1989, 30, 5393.
C6H11 SO2Ph 98
15. (a) Belakhov, V. V.; Yudelevich, V. I.; Komarov, E. V.; Ionin,
B. I.; Petrov, A. A., J. Gen. Chem. USSR (Engl. Transl.) 1984, 920.
adamantyl SO2Ph 94
(b) Devedjiev, I.; Ganev, V.; Borisov, G.; Zabski, L.; Jedlinski, Z.,
Phosphorus Sulfur Silicon 1989, 42, 167.
adamantyl P(O)(OEt)2 97
16. (a) Dhawan, B.; Redmore, D., J. Chem. Res. (S) 1988, 34. (b) Synthetic
Methods of Organic Chemistry; Theiheimer, W., Ed.; Karger: Basel,
Jang and Cho45 have subsequently applied this methodology
1971; Vol. 25, p 357. (c) Kapura, A. A.; Shermergon, I. M., J. Gen.
to the formation of intermolecular carbon-carbon bonds in water.
Chem. USSR (Engl. Transl.) 1989, 1137.
They have found that this reaction requires the addition of indium
17. Kabachnik, M. J.; Shipov, A. E.; Mastrjukova, T. A., Izv. Akad. Nauk
metal in order for addition to the alkene to take place. They have
SSSR, Ser. Khim. 1960, 146.
also found that under aqueous conditions addition of cyclohexyl
18. (a) Gallagher, M. J.; Honegger, H., Aust. J. Chem. 1980, 33, 287.
radicals, generated from cyclohexyl iodide (39), to an ą,�-enone
(b) Bailie, A. C.; Cornell, C. L.; Wright, B. J.; Wright, K., Tetrahedron
40 produces the 1,4-addition product 41 regioselectively, whereas
Lett. 1992, 33, 5133.
allylindium reagents generate the 1,2- or 1,4-addition product,
19. Entwistle, I. D.; Johnstone, R. A. W.; Telford, R. P., J. Chem. Res. (S)
depending on the substrate, under ionic conditions (eq 23). 1977, 117.
20. Cates, L. A.; Li, V. S., Phosphorus Sulfur 1984, 21, 187.
21. Devedjiev, I.; Ganev, V.; Stefanova, R.; Borissov, G., Phosphorus Sulfur
In, EPHP
O O
1988, 35, 261.
CTAB, ABCVA
I
H2O, 80 �C
22. Devedjiev, I.; Ganev, V.; Borissov, G., Eur. Polym. J. 1988, 24, 475.
(23)
89%
23. Tyka, R.; H�gele, G., Phosphorus Sulfur Silicon 1989, 44, 103.
24. Hamilton, R.; Walker, B.; Walker, B. J., Tetrahedron Lett. 1995, 36,
39 40
4451.
25. Cristau, H. J.; Monbrun, J.; Tillard, M.; Pirat, J. L., Tetrahedron Lett.
41
2003, 44, 3183.
26. DeprŁle, S.; Montchamp, J. L., J. Organomet. Chem. 2002, 643, 154.
27. Hicks, L. D.; Han, J. K.; Fry, A. J., Tetrahedron Lett. 2000, 41, 7817.
28. Gordon, P. E.; Fry, A. J., Tetrahedron Lett. 2001, 42, 831.
29. Fry, A. J.; Allukian, M.; Williams, A. D., Tetrahedron 2002, 58,
4411.
1. Yudelevich, V. I.; Sokolov, L. B.; Ionin, B. I., Russ. Chem. Rev. (Engl.
30. Barton, D. H. R.; Jang, D. O.; Jaszberenyi, J. C., Tetrahedron Lett. 1992,
Transl.) 1980, 49, 46.
33, 5709.
2. (a) Wulfman, D. S., In The Chemistry of Diazonium and Diazo Groups;
31. Barton, D. H. R.; Jang, D. O.; Jaszberenyi, J. C., J. Org. Chem. 1993,
Patai, S., Ed.; Wiley: New York, 1978; Part 1, p 286. (b) Fieser, M.;
58, 6838.
Fieser, L. F., Fieser & Fieser 1967, 1, 489.
32. Jang, D. O., Tetrahedron Lett. 1996, 37, 5367.
3. (a) Nasielski, J.; Moucheron, C.; Nasielski-Hinkens, R., Bull. Soc. Chim.
33. Jang, D. O.; Song, S. H., Tetrahedron Lett. 2000, 41, 247.
Belg. 1992, 101, 491. (b) Nasielski-Hinkens, R.; Leveque, P.; Castelet,
D.; Nasielski, J., Heterocycles 1987, 26, 2433. 34. DeprŁle, S.; Montchamp, J.-L., J. Org. Chem. 2001, 66, 6745.
Avoid Skin Contact with All Reagents
6 HYPOPHOSPHOROUS ACID
35. Pat. 97-EP2284 970506 (to Calderon, J. M. B.; Chicharro, G. J.; 40. Yorimitsu, H.; Shinokubo, H.; Oshima, K., Bull. Chem. Soc. Jpn. 2001,
Fiandorn, R. J.; Huss, S.; Ward, R. A.). 74, 225.
36. McCague, R.; Pritchard, R. G.; Stoodley, R. J.; Williamson, D. S., Chem. 41. Reding, M. T.; Kaburagi, Y.; Tokuyama, H.; Fukuyama, T., Heterocycles
Commun. 1998, 2691. 2002, 56, 313.
37. Graham, S. R.; Murphy, J. A.; Coates, D., Tetrahedron Lett. 1999, 40, 42. Reding, M. T.; Fukuyama, T., Org. Lett. 1999, 1, 973.
2415.
43. Kita, Y.; Nambu, H.; Ramesh, N. G.; Anilkumar, G.; Matsugi, M., Org.
38. Graham, S. R.; Murphy, J. A.; Kennedy, A. R., J. Chem. Soc., Perkin Lett. 2001, 3, 1157.
Trans. 1 1999, 3071.
44. Jang, D. O.; Cho, D. H.; Chung, C. M., Synlett 2001, 1923.
39. Yorimitsu, H.; Shinokubo, H.; Oshima, K., Chem. Lett. 2000, 104.
45. Jang, D. O.; Cho, D. H., Synlett 2002, 631.
A list of General Abbreviations appears on the front Endpapers