Ring-closing metathesis in an enantioselective synthesis of the macrocyclic core of crassin acetate

Abstract

The formation of the macrocyclic core of crassin acetate from an acyclic precursor could be effected by ring-closing alkyne metathesis reactions while ring-closing olefin metathesis reactions failed. Installment of necessary stereochemistry was achieved by Sharpless asymmetric epoxidations on allylic alcohols obtained from geranyl acetate or farnesyl acetate. The macrocyclic core of crassin acetate could thus be made from geranyl or farnesyl acetate in 12 steps with a total yield of 6.7% and 11.0%, respectively.