4-Benzyl-2,3-didehydroprolinate as a homochiral template for Michael additions. Synthesis of enantiopure α-allokainoids, β-kainoids, 2,3-methanoprolines and other 3,4-disubstituted prolines

Article abstract of DOI:10.1016/0957-4166(96)00336-9

Ethyl (4R)-N-methoxycarbonyl-4-benzyl-2,3-didehydroprolinate 10a undergoes Michael additions with stabilized carbanions and cuprates giving exclusively the enantiopure all-trans 3,4-disubstituted prolinates. The high stereoselection observed in this reaction is driven by the C-4 substituent of the Michael acceptor. This methodology has been applied to the synthesis of the enantiopure β-kainoid 5a and the 2,3-methanoproline 15.