C_2-Symmetric Cu(II) Complexes as Chiral Lewis Acids. Catalytic, Enantioselective Cycloadditions of Silyl Ketenes

摘要

C_2-Symmetric bis(oxazoline)-Cu(II) complexes (4a-g) catalyze the enantioselective [2 + 2] cycloaddition between (silyl)ketenes and chelating carbonyl substrates. A range of substituted #beta#-lactones can be produced in excellent yields and selectivities. It was also found that (trimethylsilyl)-ketne (1) may also undergo a highly selective hetero Diels-Alder reaction with #beta#, #gamma#-unsaturated #alpha#-keto esters.