OXIDATION OF 1-ARYLCYCLOHEXA-2,5-DIENES AND SUBSEQUENT DOUBLE MICHAEL ADDITION. A RAPID ACCESS TO THE BUCHI KETONE AND THE PENTACYCLIC CORE OF ASPIDOSPERMA ALKALOIDS

The Pd-catalyzed oxidation of 1-arylcyclohexa-2,5-dienes, resulting from a Birch reductive allcylation, leads to the corresponding arylcyclohexadienones. A careful choice of the substituents on the starting biaryl affords arylcyclohexadieonones, which may then enter into a double Michael addition, opening an access to the tetracyclic core of terpene indole alkaloids of the aspidosperma family. This strategy was used to prepare the Buchi ketone, a key-intermediate in the synthesis of this class of alkaloids, in 6 synthetic operations and 17% overall yield from commercially available 2-aminobiphenyl.