Abstract
During the course of total synthesis of natural products, synthetic chemists would frequently encounter serious problems that require either development of new synthetic methodologies or novel designs in synthetic routes. In this context, the total synthesis of antibiotic 593 A could be completed because of p-methoxymethoxyphenylamine, a novel and practical protecting group for β-lactams. Reduction of thiolesters to aldehydes by means of triethylsilane and palladium on carbon could be discovered fortuitously during the total synthesis of porothramycin B. In order to carry out a biomimetic total synthesis of vincadifformine using our first-generation indole synthe-sis, we developed the chemistry of 2, 4-dinitrobenzenesulfonamides which could be deprotected under extremely mild conditions. More stable 2-nitrobenzenesulfonamides now finds widespread use for preparation of secondary amines from primary amines. Failure to introduce an sp3 carbon to the 2-position of indoles by means of the first-generation protocol forced us to develop another one in which o-alkenylthioanilides undergo radical cyclization to give 2, 3-disubstituted indoles. Combination of the second-generation indole synthesis and the chemistry of nitrobenzenesulfon-amide culminated in the first de novo total synthesis of ( ) -vinblastine.
