α,β-unsaturated nitriles: stereoselective conjugate addition reactions

摘要

Dithiane anions undergo intramolecular conjugate additions with α,β-unsaturated nitriles when a dithiane anion is tethered to N-1 of the 3-cyanol-1,4,5,6,-tetrahydropyridine nucleus. 3-Cyano-l- [2-(1,3-dithianyl-2-yl)ethyl]-1,4,5,6-tetrahydropyridine (1a) and the one-carbon homologue 1b cyclize in the presence of 12-crown-4 to generate indolizidine 3 and quinolizidine 9, in which the nitrile group exhibits a strong, thermodynamic preference for the axial orientation.