Yoshiro Kobayashi

Asymmetric trifluoromethylation of aldehydes and ketones with trifluoromethyltrimethylsilane catalyzed by chiral quaternary ammonium fluorides

Abstract The trifluoromethylation of aldehydes and ketones with trifluoromethyltrimethylsilane catalyzed by chiral quarternary ammonium fluorides was carried out enantioselectively to give optically active 1-substituted-2,2,2-trifluoroethanols.

ASYMMETRIC ALLYLATION WITH CHIRAL FORMAMIDE CATALYSTS

Abstract The successful example of chiral formamides that function as asymmetric catalysts is described. (S,S)-N,N-Bis(α-methylbenzyl)formamide mediates the enantioselective addition of allyl- and crotyltrichlorosilanes to aliphatic aldehydes with the assistance of hexamethylphosphoramide (HMPA) to afford the corresponding homoallylic alcohols in up to 98% enantiomeric excess.

ASYMMETRIC ALLYLATION OF AROMATIC ALDEHYDES CATALYZED BY CHIRAL PHOSPHORAMIDES PREPARED FROM (S)-PROLINE

Abstract Chiral phosphoramides prepared from (S)-proline were used to catalyze the allylation and crotylation of aromatic aldehydes with allylic trichlorosilanes in good enantioselective yields. Phosphoramides 4d and 4m gave chiral homoallylic alcohols and their enantiomers, respectively, with similar levels of enantioselectivity.

A chiral formamide: Design and application to catalytic asymmetric synthesis

Abstract ( S , S )- N , N -Bis(-α-methylbenzyl)formamide is the first example of chiral formamides that function as Lewis base catalysis to effectively serve catalytic asymmetric synthesis. The chiral formamide in combination with an additive, HMPA, catalyzes allylations of aliphatic aldehydes with allyl- and crotyltrichlorosilanes with high enantioselectivity (up to 98% ee). In the crotylations with ( E )-crotyltrichlorosilane, cyclohexanecarboxaldehyde and hydrocinnamaldehyde gave the corresponding anti homoallylic alcohols exclusively with 98 and 94% ees, respectively.

Diastereoselective trifluoromethylation of chiral imide enolates with iodotrifluoromethane mediated by Triethylborane

Abstract The trifluoromethylation of lithium enolates of chiral N-acyloxazlidinones with iodotrifluoromethane mediated by triethylborane proceeds with good diastereomeric excess (62–86% de).

Asymmetric allylation of aldehydes catalyzed by substoichiometric amounts of chiral phosphoramides

Abstract The asymmetric allylation and crotylation of aromatic aldehydes with allylic trichlorosilanes catalyzed by substoichiometric quantities of chiral phosphoramides were carried out with good enantiomeric excess (up to 88% ee). Phosphoramides 3 and 4 , prepared from (S)-proline, gave chiral homoallylic alcohols 6 and their enantiomers 7 , respectively, with similar levels of enantioselectivity.

Isolation of α,α-difluoroketene silyl acetal and its application to asymmetric aldol reactions

Abstract Salt-free α,α-difluoroketene silyl acetal 1 was prepared in pure form. Aldol reactions of 1 with aldehydes catalyzed by catalytic amounts of chiral Lewis acids 2 and 3 proceeded with excellent enantiomeric excess to give optically active α,α-difluoro-β-hydroxy esters 4–11 (up to 98% ee).

Asymmetric allenylation of aliphatic aldehydes catalyzed by a chiral formamide

Abstract ( S , S )- N , N -Bis(α-methylbenzyl)formamide in combination with HMPA catalyzes the allenylation of aliphatic aldehydes with propargyltrichlorosilane with good enantioselectivity (up to 95% e.e.).

Diastereoselective trifluoromethylation of chiral imide enolates with iodotrifluoromethane mediated by triethylborane

Abstract The trifluoromethylation of lithium enotates of chiral N-acyloxazolidinones with iodotriftuoromcthane mediated by triethylborone proceeds with good diastereomeric excess.

Asymmetric aldol addition of aldehydes to a difluoroketene silyl acetal catalyzed by chiral Lewis acids

Abstract Aldol reaction of aldehydes with difluoroketene ethyl trimethylsilyl acetal (1) in the presence of a substoichiometric amount of chiral Lewis acid 2 or 3 provides the corresponding α,α-difluoro β-hydroxy esters 4–12 with high enantioselectivities (up to 98% ee). Reaction temperature has a great influence on the enantiofacial selection of aldehydes; the reactions of benzyloxyacetaldehyde catalyzed by Lewis acid 2 at −78 and −30°C gave the (+)- and (−)-α,α-difluoro β-hydroxy esters 7 in optical yields of 98% and 85%, respectively.