Chiral quaternary benzophenone hydrazonium salt derivatives; Efficient chiral catalysts for the enantioselective phase-transfer alkylation of imines. Application to synthesis of chiral primary amines

Abstract

(2S)-1-Methyl-1-[N-(diphenylmethylene)]-2-hydroxymethylpyrrolidine hydrazonium iodide I-a has been designed to catalyse the enantioselective phase-transfer alkylation of N-(diphenylmethylene) benzenemethanamine II . Although the weak acidic character of the latter, alkylations have been performed within reasonable reaction times. Optically active primary amines III a-e have been prepared in good chemical yields and up to 94% e.e. using 2–5 mol-% of the chiral catalyst only.