Highly diastereoselective formation of substituted indolizidines and quinolizidines by radical cyclization
摘要:
2-Substituted 2,3-dihydro-4-pyridinones (eg., 1a) bearing an (omega-bromoacyl)-, (o-bromoaroyl)-, or (o-bromophenyl)aeetyl group on nitrogen, when treated with tributylstannane, undergo highly diastereoselective cyclization by intramolecular homolytic addition anti to the substituent at C-2; molecular mechanics calculation support the view that the diastereoselectivity arises from the nonbonded interaction between the substituent and the amide carbonyl group.