A short synthetic route towards merosesquiterpenes with a benzoxanthene skeleton

A short synthetic sequence for the preparation of merosesquiterpenes with a benzoxanthene skeleton starting from commercial (-)-sclareol is reported. The D ring of the target compound is obtained through a Diels-Alder cycloaddition, involving a dienoldiether derived from a tricyclic alpha, beta-enone synthesized in two steps from the starting diterpene. Utilizing this procedure, the preparation of (+)-hongoquercin A and the first synthesis of (+)-cyclospongiaquinone-1 were achieved.