Total Syntheses of (±)-(Z)- and (±)-(E)-9-(Bromomethylene)-1,5,5-trimethylspiro[5.5]undeca-1,7-dien-3-one and (±)-Majusculone

A new total synthesis of the chamigrene sesquiterpenoids (Z)-9-(bromomethylene)-1,5,5-trimethylspiro[5.5] undeca-1,7-diene-3-one and its 15-E-epimer has been accomplished in 13 steps. In our sequence, a Diels-Alder reaction and subsequent reductive alkylation of the resulting adduct was utilized as the key strategy to create the A-ring and the quaternary spirocenter with the suitable functionalities for accessing the B-ring. Additionally, from the advanced intermediate, a total synthesis of (+/-)-majusculone, a nor-chamigrene natural product, was also readily achieved in two steps.