Synthesis of Four Possible Isomers of 9-(Bromomethylene)-1, 2, 5-trimethylspiro[5.5]undeca-1, 7-dien-3-one : Structure Elucidation of a Brominated Rearranged Chamigrane-Type Sesquiterpene

The first total synthesis of (5R*, 6R*)- and (5R*, 6S*)-9-(bromomethylene)-1, 2, 5-trimethyl-spiro[5.5]undeca-1, 7-dien-3-one (1a and 1b) was achieved stereoselectively. The relative configuration of C-5 and C-6 of the natural product Z-1 was elucidated as 5R* and 6R* by comparison with our synthetic samples.