Metal enolates of alpha-CF3 ketones: theoretical guideline, direct generation, and synthetic use

The difficulty as well as the significance of the direct generation of metal enolates of alpha-CF(3) ketones cannot be easily understood by chemists unfamiliar with F. In sharp contrast to the sunny side of non-F, hydrocarbon chemistry, F chemistry has long been overshadowed. Metal enolates of carbonyl compounds are synthetically important in C-C bond-forming reactions. However, the metal enolates of fluorinated carbonyl compounds have been severely limited to alpha-F metal enolates. Alpha-CF(3) metal enolates have generally been recognized as unstable and difficult to prepare because of the facile beta-M-F elimination. However, we have developed a direct generation and synthetic application of alpha-CF(3) metal enolates. Therefore, the present results regarding the direct generation and synthetic use of metal enolates of alpha-CF(3) ketones might be recognized as a real breakthrough for the general use of metal enolates in F chemistry.     

Alkylation and aldol reactions of acyl derivatives of N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine: asymmetric synthesis of α-alkoxy-, α-substituted-β-alkoxy- and α,β-dialkoxyaldehydes

Treatment of a range of O-protected glycolate derivatives of the chiral auxiliary N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine with KHMDS in the presence of 18-crown-6 followed by addition of an alkyl halide generates α-substituted derivatives with very high levels of diastereoselectivity. Alternatively, reaction of the potassium enolate of a propanoate or O-protected glycolate derivative of N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine with a range of aldehydes gives syn-aldol products with high levels of diastereoselectivity. These adducts may be reductively cleaved with LiAlH₄ to give enantiopure α-alkoxy-, α-substituted-β-alkoxy- and α,β-dialkoxyaldehydes in good yield.