THE CHEMISTRY OF TAXANES - SKELETAL REARRANGEMENTS OF BACCATIN DERIVATIVES VIA RADICAL INTERMEDIATES

In the course of a synthetic program aimed at systematic defunctionalization of the taxol core for structure activity studies, a number of radical-based deoxygenation reactions were carried out on baccatin III derivatives. In this connection, we have discovered that formation of radicals at positions C-1, C-2, and C-7 in the taxane core of baccatin III results in a number of skeletal rearrangement cascades. Furthermore, the exact composition of the product mixture depends on the specific tin (or silicon) hydride used for the reduction. In the case of C-2- and C-7-derived radicals, direct quenching with tin hydrides without rearrangement was possible under some conditions. However, we were unable to find conditions to quench the C-1 radical, since rearrangement pathways always predominate in this case.