N-Benzyl-Protection of Amino Acid Derivatives by Reductive Alkylation with α-Picoline-Borane

Abstract

A convenient method for N-protection of amino acid derivatives with a benzyl group by reductive alkylation of amino acid derivatives with α-picoline-borane is described. Amino acid esters or amino alcohols were treated with aryl aldehydes in methanol/acetic­ acid in the presence of α-picoline-borane to give N-benzyl-protected amino acid derivatives in good yields.

Key words

amino acid esters - amino alcohols - benzylation - protecting groups - reductions

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9

Thermal stabilities of α- and γ-picoline-borane were examined. They were non-explosive at 100 ˚C and did not decompose under ambient conditions over two years judging from the HPLC analysis of the products.