Semisynthesis of Taxol: A Highly Enantio‐ and Diastereoselective Synthesis of the Side Chain and a New Method for Ester Formation at C13 Using Thioesters

The production of Paclitaxel (taxol, 2) on an industrial scale may be possible with a novel semisynthesis relying on the readily accessible 10-deacetylbaccatin III and the side-chain unit 1. The crucial factor is the remarkably high yield for the 13-O-acylation of the terpene framework, which is usually very difficult. Thioester 1 can be prepared fairly directly with the desired relative and absolute configuration by addition of the appropriate boron enolate to an imine.