Stereo- and regiocontrol in intermolecular [2+2] cycloadditions between diarylketenes and allenamides to access substituted α-methylenecyclobutanones.

The development of intermolecular [2+2] cycloadditions between allenamides and diarylketenes is described. α-Aryldiazo arylketones are employed as ketene precursors that react smoothly with allenamides in the presence of a P(C 6 F 5 ) 3 promoter. High diastereoselectivity (dr > 20 : 1) with endo-regioselectivity can be achieved when two aryl groups of ketenes have opposite electronic properties. The role of P(C 6 F 5 ) 3 is to increase the reaction yields, but also enhancing stereoselectivity.