Radical induced fragmentation in a benzoxocane ring system: application to the synthesis of elvirol and a formal synthesis of 7,8-dihydroxycalamenene

A novel radical induced fragmentation in a benzoxocane ring system has been employed for a synthesis of elvirol 8 and an advanced intermediate in the synthesis of 7,8-dihydroxycalamenene 20. The coumarins 9, 22 were taken through a sequence of reactions to the benzoxocanols 16, 30, which when subjected to Barton’s deoxygenation conditions involving conversion to the corresponding thionocarbonates 17, 31 followed by exposure to tri-n-butyltin hydride, underwent a radical induced fragmentation to furnish elvirol 8 and the curcuphenol derivative 32, which was converted to the dimethoxy compound 33. This had served as an advanced intermediate in a previous synthesis of dihydroxycalamenene.