A facile entry into the ring system of sativene

The mechanism of the dehydrobromination of two isomeric dibromo-cis-4a-methyldecalin-2,5-diones and tribromo-cis-4a-methyldecalin-2,5-dione is described. Treatment of dione ( 2 ), with 2 equiv of bromine gave a mixture of dibromides ( 3 ) and ( 4 ) in a 1:1 ratio. Treatment of ( 2 ) with 3.2 equiv of bromine gave tribromide ( 5 ) as the major product. Dehydrobromination of ( 3 ) and ( 4 ), independently with DBU in THF, resulted in the loss of HBr and the exclusive formation of two isomeric tricyclic compounds ( 6 ) and ( 7 ) respectively. Dehydrobromination of tribromide ( 5 ) with DBU gave a mixture of two tricyclic compounds ( 6 ) and ( 8 ) in an approximate ratio of 1:1. The mechanisms of the formation of the isomeric tricyclic bromoketones ( 6 ) and ( 7 ) from compounds ( 3 ) and ( 4 ), and that of ( 6 ) and ( 8 ) from the tribromide ( 5 ) are discussed. Both tricyclic compounds ( 6 ) and ( 8 ), readily available in good yields from Wieland Miescher ketone ( 1 ), have the same carbon skeleton as the sesquiterpene hydrocarbon sativene.