M. Nakajima et al. / Tetrahedron Letters 43 (2002) 8827–8829
8829
3
. (a) Andrews, G. C.; Crawford, T. C.; Contillo, L. G.
Tetrahedron Lett. 1981, 22, 3803–3806; (b) Bonini, C.;
Righi, G. Synthesis 1994, 225–238; (c) Garrett, C. E.; Fu,
G. C. J. Org. Chem. 1997, 62, 4534–4535.
drogenphosphate aq., and extracted with ethyl acetate (50
mL). The organic layer was washed with brine (20 mL),
dried over sodium sulfate and concentrated. The crude
material was purified by column chromatography (silica
gel, 5 g, hexane/AcOEt=10:1) to give 2-chloro-1,2-
diphenylethanol (57 mg, 96%). HPLC (AD-H, hex/2-
propanol=29:1): tR (1S,2S)-(+)-isomer, 22.0 min
4
5
. Denmark, S. E.; Barsanti, P. A.; Wong, K.-T.; Stavenger,
R. A. J. Org. Chem. 1998, 63, 2428–2429.
. For enantioselective allylations via silicate complexes cat-
alyzed by chiral Lewis bases, see: (a) Denmark, S. E.;
Coe, D. M.; Pratt, N. E.; Griedel, B. D. J. Org. Chem.
(
95.1%); (1R,1R)-(−)-isomer, 24.0 min (4.9%).
1
1
0. Fu and co-workers reported that the presence of diiso-
propylethylamine is important for higher enantioselectiv-
ity and more reproducible results.
1
994, 59, 6161–6163; (b) Iseki, K.; Kuroki, Y.; Taka-
hashi, M.; Kobayashi, Y. Tetrahedron Lett. 1996, 37,
149–5150; (c) Iseki, K.; Mizuno, S.; Kuroki, Y.;
5
1. In our early work on allylation of aldehyde with allyl-
trichlorosilane catalyzed by 1, addition of diisopropyl-
ethylamine was effective for rate acceleration wherein the
amine promotes a dissociation of N-oxide from the sili-
con atom in the product by ligand exchange to regenerate
N-oxide. In the present reaction, little rate acceleration
Kobayashi, Y. Tetrahedron Lett. 1999, 39, 2767–2770; (d)
Shimada, T.; Kina, A.; Ikeda, S.; Hayashi, T. Org. Lett.
2
002, 4, 2799–2801; (e) Malkov, A. V.; Orsini, M.; Per-
nazza, D.; Muir, K. W.; Langer, V.; Meghani, P.; Kocov-
sky, P. Org. Lett. 2002, 4, 1047–1049.
. For enantioselective aldol reactions via silicate complexes
catalyzed by chiral Lewis bases, see: Denmark, S. E.;
Stavenger, R. A. Acc. Chem. Res. 2000, 33, 432–440.
. Tao, B.; Lo, M. M.-C.; Fu, G. C. J. Am. Chem. Soc.
6
12
was observed. An NMR study revealed that dissocia-
tion of N-oxide from the product is so fast that the
benefit of ligand exchange by diisopropylethylamine is
negligible.
7
8
2
001, 123, 353–354.
1
1
2. In the case of the allylation, the complex of the silyl ether
of the allylated product with the N,N%-dioxide was
. (a) Nakajima, M.; Saito, M.; Shiro, M.; Hashimoto, S. J.
Am. Chem. Soc. 1998, 120, 6419–6420; (b) Nakajima, M.;
Saito, M.; Hashimoto, S. Chem. Pharm. Bull. 2000, 48,
1
observed in H NMR spectrum before the addition of
diisopropylethylamine and the signals of the free N,N%-
dioxide appeared upon the addition of amine. On the
other hand, the free N,N%-dioxide was observed in the
epoxide opening even in the absence of amine.
3
06–307; (c) Saito, M.; Nakajima, M.; Hashimoto, S.
Chem. Commun. 2000, 1851–1852; (d) Nakajima, M.;
Yamaguchi, Y.; Hashimoto, S. Chem. Commun. 2001,
1
596–1597.
3. Racemic N-oxides were prepared by palladium-catalyzed
coupling of 2-chloroisoquinoline and 2-methyl- or 2-
methoxy-1-naphthylborate followed by oxidation with
mCPBA. Optical resolution through the hydrogen com-
plex with homochiral binaphthol ((R)-binaphthol for 8
and (S)-binaphthol for 9) afforded optically pure 8 (mp
9
. Representative procedure: To a stirred solution of 2 (7.5
mg, 10 mol%), cis-stilbene oxide 3 (50 mg) and diiso-
propylethylamine (33 mg, 1.5 equiv.) in dichloromethane
(1
mL) was added
l
M
tetrachlorosilane in
dichloromethane (0.50 mL, 2.0 equiv.) at −78°C under an
argon atmosphere. The mixture was stirred at the same
temperature for 6 h. After the reaction was quenched
with satd sodium bicarbonate aq. (2 mL), the aqueous
layer was treated with potassium fluoride/potassium dihy-
2
1
2
1
13.5–214.5°C, [h] =−30.8 (c 1.0, CHCl )) and 9 (mp
D 3
21
80.5°C, [h] =+132.1 (c 0.9, CHCl )). Absolute configu-
D
3
rations of 8 and 9 have not been determined.