Mercuric Trifluoroacetate Mediated Brominative Cyclizations of Dienes. Total Synthesis of dl-3β-Bromo-8-epicaparrapi Oxide

Mercuric trifluoroacetate induces the electrophilic cyclization of homogeranic acid and diene alcohols 10 with concomitant carbon-carbon bond formation to generate the bicyclic organomercury compounds 2 and 12. The mercury substituent can be stereospecifically replaced by bromine with either retention or inversion of configuration to give the bromides 1 or 4 and 11 or 14, respectively. Application of this net brominative cyclization to a synthesis of dl-3β-bromo-8-epicaparrapi oxide (15) in seven steps and 12% yield from geranylacetone is described.