Cycloadditions of o-quinone dimethides with p-quinol derivatives: regiocontrolled formation of anthracyclic ring systems

Regioselective cycloadditions between the cyclohexadienones 12–14 and the ortho-quinone dimethide 19, which is thermally generated from the corresponding 1,3-dihydro-1-methoxy-2,2-dioxide benzo[c]thiophene 27, are reported. The synthetic sequence provides rapid access to highly substituted anthracyclic system and may be of use for construction of the natural product (+)-rishirilide B.