[reaction: see text] Enantiomerically pure 2,2,3,4,5-pentasubstituted pyrrolidines can be prepared, in high overall yield, from alpha,beta-unsaturated esters. Asymmetry is introduced via a Michael addition, and additional stereogenic centers are introduced by an aldol reaction. A novel stereospecific ring-forming reaction, proceeding via a thiiranium (episulfonium) ion, yields pyrrolidines from beta-hydroxy sulfides. In this manner, 2,2,3,4,5-pentasubstituted pyrrolidines, containing three contiguous stereogenic centers around the ring, can be prepared in 44% overall yield from ethyl crotonate.

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Conjugate Addition of Organocuprates to Diethyl Vinylphosphonate. -The methodology allows a rapid entry to a variety of functionalized phosphonates in a one-pot process. -(BALDWIN, I. C.; BECKETT, R. P.; WILLIAMS, J. M. J.; Synthesis (1996) 1, 34-36; Dep. Chem., Univ. Loughborough, Loughborough, Leicestershire LE11 3TU, UK; EN)