An Opened Route to 1,3-Dimethylenecyclobutanes via Sequential Ruthenium-Catalyzed [2 + 2] Cycloaddition of Allenyl Boronate and Palladium Suzuki Coupling

The regioselective head-to-head [2 + 2] cyclodimerization of allenyl boronate catalyzed by the ruthenium catalyst [Cp*RuCl(COD)] leads to a novel diboronated 1,3-dimethylenecyclobutane. Consecutive palladium-catalyzed C−C couplings open a route to novel disubstituted 1,3-dimethylenecyclobutane species. The X-ray crystalline structure of the phenyl-substituted 1,3-dimethylenecyclobutane is provided.