Total synthesis of (+)-quassin

A total synthesis of (+)-quassin from naturally occurring (S)-(+)-carvone i s described. The total number of steps was 28, and the overall yield was ab out 2.6%. The synthetic strategy for the construction of the tetracyclic ca rbon framework was based on a C-->ABC-->ABCD ring annulation sequence, invo lving an aldol reaction, an intramolecular Diels-Alder reaction, and an int ramolecular acylation as the key steps. Subsequent functionalization of rin g A and ring C then afforded the target (+)-quassin.