Providencin is a highly oxygenated diterpenoid found in the sea plume Antillogorgia Kallos. It features a previously undescribed bicyclo[12.2.0]undecane carbon skeleton containing a tetrasubstituted cyclobutane ring, two trans-fused epoxides and a butenolide moiety. The absolute configuration of providencin remains to be proven. Biological testing revealed modest cytotoxic activity against several human cancer cell lines. This work presents the synthesis of an important building block en route to providencin based on a new retrosynthetic approach. Key steps are an enantioselective Lewis acid-catalyzed cycloaddition reaction to form the cyclobutane ring, a copper-assisted Stille-coupling under very mild conditions and the regioselective deprotection of just one of two trityl protecting groups.