Stereocontrolled entry to the tricyclo[3.3.0]oxoheptane core of bielschowskysin by a [2+2] cycloaddition of an allene-butenolide

As part of ongoing transannulation studies, the practical synthesis of an allene-linked γ-butenolide from l-malic acid and its substrate-controlled [2+2] photocycloaddition to the tricyclic core of bielschowskysin (1) are described.