C(2)-symmetric Cu(II) complexes as chiral lewis acids. Catalytic, enantioselective cycloadditions of silyl ketenes.
[reaction: see text] 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)ketene (1) may also undergo a highly selective hetero Diels-Alder reaction with beta,gamma-unsaturated alpha-keto esters.
Evans
D A
DA
Department of Chemistry & Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA. evans@chemistry.harvard.edu
Janey
J M
JM