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Communication | Special issue | Vol 66, No. 1, 2005, pp.31-37
Published online, 10th June, 2005
DOI: 10.3987/COM-05-S(K)3
■ Enantioselective Synthesis of (R)-1-Azaspiro[4.4]nonane-2,6-dione Ethylene Ketal, Key Chiral Intermediate in the Elaboration of (-)-Cephalotaxine

Mathieu Pizzonero, Françoise Dumas,* and Jean d’Angelo*

*Department of Organic Chemistry, BioCIS, UMR 8076 CNRS, School of Pharmacy, Paris XI University, 5, Rue Jean-Baptiste Clément, 92296 Châtenay-Malabry Cedex, France

Abstract

An enantioselective synthesis of (R)-1-azaspiro[4.4]nonane-2,6-dione ethylene ketal (4), chiral relay in the elaboration of (-)-cephalotaxine (1b), starting from (R)-1-(2-methoxycarbonylethyl)-2-oxo-cyclopentanecarboxylic acid methyl ester ((R)-10) (8 chemical operations, 26% overall yield, ee > 95%) is described. The Curtius rearrangement of acyl azide (12) was used as the key strategic element to install with a perfect stereochemical fidelity and a high efficiency an α-nitrogen substituent at the quaternary carbon center in 10.