Diastereoselective Alkylation of Chiral Glycinate Derivatives Containing the α–Phenylethyl Group

Cristina Rodríguez–Garnica, Heraclio López–Ruiz,* Susana Rojas–Lima, Alejandro Álvarez–Hernández, Rafael Tapia–Benavides, and María Concepción García–López

Área Académica de Química, Ciudad Universitaria Carretera Pachuca–Tulancingo Km. 4.5. Mineral de la Reforma, Hidalgo, México.*heraclio@uaeh.edu.mx

Received October 1, 2010.
Accepted February 28, 2011.

Abstract

Novel chiral glycinate derivatives (S)–6 and (S)–7 containing the α–phenylethyl group, were prepared and studied as potential precursors of enantiopure α–substituted–α–amino acids. In particular, the alkylation of enolate (S)–7–Li showed substantial (78:22 dr) stereoinduction by the N–(l–phenylethyl)benzamide chiral auxiliary. Addition of DMPU showed no appreciable effect upon the diastereoselectivity.

Keywords: Alkylation; diastereoselective; enantioselective; lithium enolates; glycinate; amino acids.

Resumen

Derivados quirales novedosos de glicinato (S)–6 y (S)–7 conteniendo el grupo α–feniletil fueron preparados y estudiados como precursores potenciales de α–aminoácidos α–sustituidos. En particular el auxiliar quiral N–(l–feniletil)benzamida mostró estereoinducción sustancial (78:22 dr) en la alquilación del enolato (S)–7–Li. La adición de DMPU no mostró un efecto apreciable en la diastereoselectividad.

Palabras clave: Alquilación, diastereoselectiva, enantioselectiva, enolatos de litio, glicinato, amino ácidos.

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Acknowledgments

We are indebted to Conacyt, Mexico for financial support via grants J49336–Q and 84453. We are indebted to Prof. Joseph M. Muchowski for many discussions.

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