A Poly(ethylene glycol)-Supported Chiral Auxiliary for Asymmetric Michael Reaction

Key words

chiral auxiliaries - Michael addition - immobilization - quaternary stereocenters - soluble polymers

Significance

Poly(ethylene glycol)-supported l-valine-derived auxiliary 1 was prepared from poly(ethylene glycol) dimesylate in four steps. After condensation with ethyl cyclopentan-2-one carboxylate and ethyl cyclohexan-2-one carboxylate, copper-catalyzed Michael reactions of the resulting enamines 2 with methyl vinyl ketone were carried out at 23 °C for two days in acetone to give ethyl (R)-2-oxo-1-(3-oxobutyl)cyclopentane carboxylate and ethyl-(R) 2-oxo-1-(3-oxobutyl)cyclohexane carboxylate with 99% ee and 97% ee, respectively. Auxiliary 1 was recovered by simple precipitation from diethyl ether.

Comment

The authors have reported that the copper-catalyzed auxiliary-mediated reaction of cyclic β-oxo esters with methyl vinyl ketone gave the Michael adducts in high yields with excellent ee under homogeneous conditions (J. Christoffers, A. Mann Chem. Eur. J. 2001, 7, 1014-1027).