1
356
J . Org. Chem. 1998, 63, 1356-1359
Asym m etr ic Ad d ition of Tr im eth ylsilyl
A variety of aromatic aldehydes and some aliphatic
aldehydes can be converted to optically active cyano-
hydrins by the catalysis of oxynitrilases.6 Catalytic
Cya n id e to Ben za ld eh yd es Ca ta lyzed by
Sa m a r iu m (III) Ch lor id e a n d Ch ir a l
P h osp h or u s(V) Rea gen ts
a
3
asymmetric addition of HCN or Me SiCN onto aldehydes
can be achieved by using chiral ligands, such as dipep-
tides (especially diketopiperazines derived from histidine
Wen-Bin Yang and J im-Min Fang*
7
f
7j
7n
and phenylalanine), bisoxazolines, salens, Schiff’s
bases,7k sulfoximines, cinchonine, and binaphthol,
7m
7g
7q
Department of Chemistry, National Taiwan University,
Taipei 106, Taiwan, Republic of China
together with Lewis acids containing Ti(IV) (most fre-
7
a
7h
7c
7p
7g
quently used), Al(III), B(III), Y(III), Sn(II), or
Received October 9, 1997
7j
Mg(II) ions. However, most of reports indicate that the
reaction must be conducted at low temperature (e.g. -78
°C) in order to obtain high enantioselectivity.
Chiral phosphorus(V) reagents have been used as
resolving agents,1 auxiliaries2 or ligands3 to promote
various asymmetric reactions. In general, those P(V)-
reagents prepared from C2-symmetric diols or diamines
do not contain asymmetric phosphorus centers. We
speculate that a bis-phosphoramidate reagent, such as
The bis-phosphoramidate 3a was prepared in 77%
overall yield by treatment of (1R,2S)-(-)-ephedrine sub-
8
a
3
sequently with POCl and ethylenediamine (Scheme 1).
The (2S,2′S,4S,4′S,5R,5′R)-configuration of 3a was un-
ambiguously determined by NMR and X-ray analyses.
A minor diastereomer 3b exhibiting the (2R,2′R,4S,-
4′S,5R,5′R)-configuration was also prepared. By a simi-
lar procedure, compound 3c (the antipode of 3a ) was
prepared from (1S,2R)-(+)-ephedrine. A preliminary
3
a , not only exhibits the advantageous effect of C2-
symmetry, but also exerts better asymmetric induction
for it contains phosphorus stereocenters closer to reactive
sites.4 In this paper, we focus on the combined use of
Lewis acid and bis-phosphoramidate reagent in promo-
tion of asymmetric cyanosilylation of benzaldehydes.
Cyanohydrins are important synthons,5 such as in
preparation of R-hydroxy acids and â-amino alcohols.
Optically active cyanohydrins can be obtained by biologi-
survey of the reaction of Me
the presence of the chiral ligand 3a indicated that Lewis
acids SmCl , SmI , LaCl , and Sc(OTf) were effective
catalysts, whereas Sm(Oi-Pr) or Ti(Oi-Pr) were inef-
fective, in terms of conversion and enantioselectivity. We
report herein mainly the SmCl -catalyzed cyanosilylation
of various benzaldehydes.9 Comparison experiments
showed that the SmCl -catalyzed cyanosilylation was
3
SiCN with benzaldehyde in
3
3
3
3
3
4
6
7
cal or chemical methods. For example, racemic cyano-
hydrins can be resolved by lipase-catalyzed acetylation.5a,6d
3
(1) Chiral P(V)-reagents as resolving agents: (a) J acques, J .; Fou-
3
quey, C.; Vitero, R. Tetrahedron Lett. 1971, 4617. (b) Mikes, F.;
Boshart, G. J . Chem. Soc., Chem. Commun. 1978, 173. (c) Arnold, W.;
Daly, J . J .; Imhof, R.; Kyburz, E. Tetrahedron Lett. 1983, 24, 343. (d)
Anderson, R. C.; Shapiro, M. J . J . Org. Chem. 1984, 49, 1304. (e)
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accelerated by addition of the bis-phosphoramidate re-
agent 3a . However, use of 3a alone (as a base) did not
promote the cyanosilylation.
1
06, 5019. (f) Alexakis, A.; Mutti, S.; Normant, J . F.; Mangeney, P.
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(
1
S. E.; Chen, C.-T. J . Am. Chem. Soc. 1992, 114, 10674. (d) Narasaka,
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1
993, 102. (f) Hanessian, S.; Andreotti, D.; Gomtsyan, A. J . Am. Chem.
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1
995, 34, 917.
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(
2
9
059. (b) Katti, K. V.; Reddy, V. S.; Singh, P. R. Chem. Soc. Rev. 1995,
7. Representative examples for using chiral P(V)-reagents as
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4
Kellogg, R. M. Tetrahedron Asymmetry 1996, 7, 2755. Representative
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O.; Fotiadu, F.; Sylvestre, M.; Buono, G. Tetrahedron Lett. 1996, 37,
3
9. (f) Denmark, S. E.; Wong, K.-T.; Stavenger, R. A. J . Am. Chem.
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8
, 73.
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(
(
(
(
a) Ohta, H.; Kimura, Y.; Sugano, Y. Tetrahedron Lett. 1988, 29, 6957.
b) Effenberger, F.; Stelzer, U. Angew. Chem., Int. Ed. Engl. 1991, 30,
8
73. (c) Warmerdam, E. G. J . C.; Brusse, J .; Kruse, C. G.; Van der
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(
1
(9) Examples for lanthanide ion-promoted asymmetric reactions: (a)
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1
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Published on Web 01/30/1998