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■ Total Synthesis of Maremycins A and D1 Using Chiral and Cyclic Nitrone with (E)-3-Ethylidene-1-methylindolin-2-one

Tohru Ueda, Mitsuhide Inada, Nobuyoshi Morita, and Osamu Tamura*

*Laboratory of Organic Chemistry, Pharmaceutical Sciences, Showa Pharmaceutical University, 3-3165, Higashi-tamagawagakuen, Machida, Tokyo 194-8543, Japan

Abstract

Total syntheses of maremycin A (4) and maremycin D1 (8) were described, featuring 1,3-dipolar cycloaddition of a chiral cyclic nitrone 15 with (E)-3-ethylidene-1-methylindolin-2-one (13). The cycloaddition was reversible, especially at high temperature in the presence of a Lewis acid or in a solvent possessing a high acceptor number. One of the cycloadducts was efficiently led to maremycin A (4) and maremycin D1 (8). High optical purity of 4 was confirmed by chiral HPLC comparison with ent-4 prepared from ent-15 and 13.