Synthesis of bicyclo[4.2.0]octan-2-ol, a substructure of solanoeclepin A

A sesterterpenoid solanoeclepin A (1) has a unique structure including a bicyclo[4.2.0]octane substructure, for which a new synthetic methodology is explored particularly to cyclize functionalized cyclobutane rings. An optically active (R)-carvone and a racemic cyclohexenone were each converted into the respective epoxyvinylsulfones, and then subjected to the heteroatom-directed conjugate addition (HADCA) by a lithium acetylide nucleophile. The intermediate carbanions from HADCA were used for the following epoxide opening reaction yielding the four-membered carbocyclic products.