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■ Synethetic Studies of Withanolides. Part 3. Some Approaches for the Side-Chain Lactone Synthesis by Means of γ-Coupling of Lithium Dienolates with the Steroidal 22-Aldehydes

Masaji Ishiguro, Masao Hirayama, Hiromitsu Saito, Akira Kajikawa, and Nobuo Ikekawa*

*Faculty of Engineering, Tokyo Institute of Technology, 2-12-1,Oh-Okayama, Meguro-ku, Tokyo 152-8552, Japan

Abstract

γ-Coupling of the lithium dienolates 5a-d with the steroidal 22-aldehydes 1-4 was investigated. Condensation of 5a with the (20R)-20-methoxymethyloxy-22-al 4 followed by lactonization gave the (20R,22R)-20-hydroxy-δ-lactone 13 which had the identical structure with withanolide D side-chain moiety, while the reaction of 5a with the 20-deoxy-22-al 1 gave the 22S-δ-lactone 6 which had the opposite stereochemistry at the 22-position to that of deoxywithaferin A. Attempts to invert the 22S-compounds 6 and 11 were unsuccessful. Lactonization of the 5,22,24-trienoic acid 14 gave predominantly the unsaturated γ-lactones.