Transition Metal/Base-Catalyzed Aldol Reactions of Isocyanoacetic Acid Derivatives with Prochiral Ketones, a Straightforward Approach to Stereochemically Defined β,β-Disubstituted-β-hydroxy-α-amino Acids.<sup>1</sup> Scope and Limitations
作者:Vadim A. Soloshonok、Alexey D. Kacharov、Dimitry V. Avilov、Kohki Ishikawa、Nobuya Nagashima、Tamio Hayashi
DOI:10.1021/jo9623402
日期:1997.5.1
A systematic study of the transition metal/base-catalyzed aldol reactions of methyl isocyanoacetate with a wide range of prochiral ketones, giving rise to the 4-(methoxycarbonyl)-5,5-disubstituted-2-oxazolines, has been made. The diastereoselectivity of these reactions was found to be influenced by a mix of several factors, including steric characteristic of the substituents, nature of the catalyst, electrostatic, and electron donor-acceptor type interactions. The former factor, a stereochemical discrimination between the substituents at the ketone carbon, was shown to be the most pronounced in controlling of the stereochemical outcome, which could be markedly improved with a proper choice of the catalyst. In particular, for the reactions of methyl isocyanoacetate with polyhaloalkyl aryl(alkyl) ketones, high diastereoselectivity (80-98% de) was achieved, thus allowing for straightforward and generalized access to the corresponding (2R*,3R*)-beta,beta-disubstituted-beta-hydroxy-alpha-amino carboxylic acid.