Versatile synthesis of 11-oxabicyclo[4.4.1]undeca-1,5-dienes by selective epoxidation of 1,6-disubstituted (E,Z,E)-1,3,5-hexatrienes and subsequent Cope rearrangement

1,6-Disubstituted (E,Z,E)-1,3,5-hexatrienes (1a-c, 2a-e), obtained in good yields (43-81%) by 2-fold Heck couplings of 1,2-dibromocyclopentene and 1,2 -dibromocyclohexene, respectively, with alkenes, can be oxidized regioselec tively at the central double bond with various oxidants such as dimethyldio xirane (DMDO), m-CPBA, or trifluoroperacetic acid in moderate to good yield s (45-87%). The resulting 1,2-dialkenylcyclohexene epoxides 4a-e undergo th ermal Cope rearrangements to furnish 1,6-oxygen-bridged cyclodeca-1,5-diene s 8a-e, which are 2-fold anti-Bredt bridgehead alkenes. The structure of co mpound 8a was established by X-ray analysis. The corresponding 1,2dialkenyl cyclopentene epoxides 3a-c give only 2,2-dialkenylcyclopentanones 9a,b by a n acid-catalyzed 1,2-alkenyl shift (71-100% yield) or indan derivatives 12b ,c (46-82%) resulting from elimination, 6 pi-electrocyclization, and aromat ization.