A polar effects controlled enantioselective 1,2-chlorine atom migration via a chlorine-bridged radical intermediate.
An enantioselective 1,2-chlorine atom migration was observed in the tributyltin hydride reduction of various dihalogenated dihydrocinnamic acid derivatives. It is proposed that the reduction involves the formation of a chlorine-bridged radical intermediate, followed by hydrogen atom transfer to either the beta- or the alpha-carbon. The product distribution is affected by electron-withdrawing groups in that hydrogen atom transfer to the proximate carbon is favored. Presumably, this is due to the transition state of the hydrogen delivery step being electron rich, due to the relatively electropositive tin radical. These results demonstrate a 1,2-chlorine atom migration reaction governed by polar effects.
Tan
Eng Wui
EW
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand.
Chan
Bun
B
Blackman
Allan G
AG