Enantioselective CC Bond Activation of Allenyl Cyclobutanes: Access to Cyclohexenones with Quaternary Stereogenic Centers

Chiral rhodium(I) complexes activate allenyl tert-cyclobutanols efficiently through enantioselective insertion into a CC σ bond of the cyclobutane (see scheme; cod=1,5-cyclooctadiene, DTBM=3,5-di-tert-butyl-4-methoxyphenyl). Ring expansion by this method produced cyclohexenones with quaternary stereogenic centers with excellent enantioselectivity. The catalyst loading can be decreased to just 0.1 mol % in rhodium.