ALPHA,BETA-UNSATURATED NITRILES - STEREOSELECTIVE CONJUGATE ADDITION-REACTIONS

Dithiane anions undergo intramolecular conjugate additions with alpha, beta-unsaturated nitriles when a dithiane anion is tethered to N-1 of the 3-cyano-1,4,5,6-tetrahydropyridine nucleus. 3-dithianyl-2-yl)ethyl ]-1,4,5,6-tetrahydropyridine (1a) and the one-carbon homologue 1b cycl ize in the presence of 12-crown-4 to generate indolizidine 3 and quino lizidine 9, in which the nitrile group exhibits a strong, thermodynami c preference for the axial orientation. Oxidation of Ib provides dithi ane S-oxide 10 that undergoes a highly stereoselective conjugate addit ion to provide crystalline quinolizidine 13. The X-ray structure of 13 is reported and corroborates our ''peg-in-a-pocket'' principle for st ereoselective conjugate additions with alpha,beta-unsaturated nitriles .