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

In the course of a synthetic program aimed at systematic defunctionali zation of the taxol core for structure activity studies, a number of r adical-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. Furthermo re, the exact composition of the product mixture depends on the specif ic 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 un able to find conditions to quench the C-1 radical, since rearrangement pathways always predominate in this case.