New strategy for the synthesis of 3-substituted prolines

Article abstract of DOI:10.1016/S0040-4039(96)02221-6

Ring formation involving a 5-exo trig cyclization between a zinc enolate and a non activated double bond led to cis diastereoisomer of 3-substituted prolines. This cyclization was achieved with transfer of chirality onto the C-2 carbon when nitrogen was protected by an α-methylbenzyl group. Reprotonation of the lithium enolate of cis derivative yielded the trans diastereoisomer.