Selective termination of a polyene cyclization by an internally situated allylsilane group

The cyclization of epoxides 6 and 7, incorporating the internally situated propenyl and allylsilane terminator groups respectively, has demonstrated that the allylsilane function is the far superior group for terminating the cyclization process, and does so in a highly efficient and selective manner. Thus, treatment of 6 with (i-PrO)TiCl3 afforded bicyclic alcohols 23 in 79–82% yield.