Photosensitized Oxygenation of Labda-8(17),12-diene, Labda-8(17),13-diene, and the Biformenes. Synthesis of Pumiloxide

Article abstract of DOI:10.1021/jo00320a027

Reactions of the title compounds with singlet oxygen were studied.In labda-8(17),12-diene (2; 7:3 mixture of E and Z isomers), syn addition leading to 7 (58percent) was predominant.Smaller amounts of 8 (20percent) by syn addition to (E)-2 or anti addition to (Z)-2, 9 (5percent), 10 (2,5percent), and 11(1.5percent) were also formed. (E)-Labda-8(17),13-diene ((E)-3) gave 29percent 12 and 40percent 13 by syn addition, whereas (Z)-3 gave 57percent 12 by syn addition and 19percent 13 by anti addition.In trans-biformene (5) syn attack at C-12 to give 15 (27percent), 16 (10percent), 18 (12percent), and 19 (4percent) was greatly preferred to syn attack at C-13 to give 17 (6percent).In cis-biformene (6) syn attack at C-13 to give 17 (39percent) predominated slightly over anti attack at C-12 to give 15 (13percent), 16 (8percent), 18 (4percent), and 19 (4percent).Diels-Alder reactions with singlet oxygen leading to epidioxides 20 and 21 were relatively unimportant (7percent from 5, 5percent from 6).The epidioxides were converted to the naturally occurring furanolabdane pumiloxide (22).