Conformation and configuration of humulene di- and triepoxides generated from four possible conformations of humulene 9,10-epoxide

The complete reaction of humulene 9,10-epoxide (1) with m-CPBA produced a h itherto unknown 2R*, 3R*, 6S*, 7S*, 9S*, 10S*-humulene 2,3;6,7;9,10-triepox ide (6) together with three known triepoxides (7, 8 and 9) in the ratio of 6 : 7 : 8 : 9 = 1.3 : 11.5 : 22.6 : 64.6. The configuration of 6 was determ ined by X-Ray crystallography. Intermediate products of the epoxidation rea ction, two humulene 6,7;9,10-{(2E)-6R*, 7R*, 9S*, 10S* (2) and (2E)-6S*, 7S *, 9S*, 10S* (3)} and two 2,3;9,10-diepoxides {(6E)-2S*, 3S*, 9S*, 10S* (4) and (6E)-2R*, 3R*, 9S*, 10S* (5)} were also produced in the ratio of 2 : 3 : 4 : 5 = 41 : 18 : 35 : 6), and these main conformations (CT, CC, CT and TC) were first determined by X-Ray crystallography (for 3 and 4) and NMR sp ectroscopy (for 2 and 5). The triepoxide (6) maintained the configuration c orresponding to the less stable TT conformation of 1 and the minor TT confo rmation of 3 and 5.