Ozonolysis of Phenolic Dehydroabietane Derivatives. : Syntheses of optically Active (+)-Confertifolin, (+)-Valdiviolide, (+)-Winterin, (+)-Isodrimenin, and (+)-Pallescensin A

Ozonolysis of phenolic dehydroabietane derivatives was investigated and the products obtained by cleavage of the aromatic ring were found to be determined by the hydroxyl substitution pattern of the aromatic C-ring. Ozonolysis of the 12-hydroxy compound (ferruginol (12)) gave pentanorlabdane-type compounds (14,15,and 16). Ozonolysis of the 11-hydroxy derivative (18) and/or the 14-hydroxy derivatives (19 and 20) afforded optically active drimanic sesquiterpenes ((+)-isodrimenin (8), (+)-confertifolin (7), (+)-valdiviolide (9), and (+)-winterin (10)) in one step. In this case, the mode of cleavage was different from that of 12. On the other hand, ozonolysis of the 13-hydroxy compound (3) caused cleavage in yet another manner to give the butenolide (23), which was easily converted into optically active pallescensin A (11). The mechanisms of the cleavage reactions are discussed.