Synthesis of BC ring-systems of Taxol by ring-closing metathesis

Highly functionalized BC ring-systems of Taxol((R)) having the required che mistry for the C1, C2 and C8 centers have been syn the sized using a ring-c losing metathesis (RCM) reaction as the key step. Silylene 26 and acetonide 27 were obtained in excellent yields with Schrock's and our recently repor ted catalyst. In the case of carbonate 23, a trans cyclooctene was formed w hen using Grubbs' catalyst, indicating that RCM does nut always proceed to completion of thermodynamic equilibrium.