Orthoacylimines: A New Class of Chiral Auxiliaries for Nucleophilic Addition of Organolithium Reagents to Imines.

Abstract

Imines. -A novel class of chiral auxiliaries for the nucleophilic addition of organometal compounds to imines is presented. Thus, condensation of optically active diols (I) and (XIII) with orthoformate and trimethylsilyl azide provides orthoacyl azides (III) and (XIV), resp., which smoothly undergo aza-Wittig reaction with various aldehydes in the presence of trimethylphosphine to furnish the title orthoacylimines (V), (X) and (XV). The nucleophilic addition of organometal compounds is achieved only with organo-lithium compounds, while Grignard reagents and organo-copper reagents do not react. The addition proceeds with moderate to high diastereoselectivity depending on the complexing properties of the solvent used. Acidic hydrolysis of the primary adduct [cf. (VII)] provides an effective access to enantiomerically enriched secondary amines, e.g. (VIII) and (XII). The auxiliary diol (I) is recovered in excellent yield. Derivative (XIId) is transformed into (S)-leucine in four steps. -(BOEZIO, A. A.; SOLBERGHE, G.; LAUZON, C.; CHARETTE*, A. B.; J. Org. Chem. 68 (2003) 8, 3241-3245; Dep. Chem., Univ. Montreal, Montreal, Que. H3C 3J7, Can.; Eng.) -Mischke 36-020 2003 Diastereoselective syntheses