Asymmetric total synthesis of (+)-dihydroitomanallene B and formal synthesis of (-)-kumausallene.

The first asymmetric total synthesis of (+)-dihydroitomanallene B and its two diastereomers, and the formal synthesis of (-)-kumausallene are reported. The synthesis of the former was completed in 18 steps from 1,4-butanediol (3.4% overall yield), with diastereoselective Tsuji-Trost cyclization to access cis -2,5-disubstituted-3-oxygenated THF scaffold and a Corey-White-Posner reaction to install the bromoallene moiety as the key steps. In addition, the enantioselective formal total synthesis of (-)-kumausallene involving the key Tsuji-Trost cyclization is also realized.