Synthesis of the Core Structure of Palhinine A

Abstract

We present a strategy to the core structure of the alkaloid palhinine A passing through a 2,5-difunctionalized cyclohexenone. This enone was prepared by a domino Michael/aldol condensation sequence. An allylation reaction on the cyclohexenone followed by oxy-Cope rearrangement introduced an allyl group at C3. After the generation of an aldehyde function on the terminus of the C5 substituent, an intramolecular aldol reaction led to a bicyclo[2.2.2]octanone. The five-membered ring of the core structure could be established by an intramolecular nitrile oxide-alkene [3+2]-cycloaddition. Prior to this key transformation, the keto function was converted to an alkene and the allyl group to an oxime.