Iodocyclisation of 1,4-dihydropyridines; Synthesis and reactivity of 1-iodoindolo[2,3-alpha]quinolizidines

The addition of iodine (or related species) to beta-acyl-N-alkyl- 1,4-dihyd ropyridines which possess an N-substituent with an appropriate nucleophile moiety, leads to the 3-iododihydropyridinium ions, which undergo an interna l nucleophilic attack to give, regio- and stereoselectively, the iodobi(pol y)heterocyclic ring systems 2a-f in good yields. Reactivity studies on the iodoindolo-quinolizidines 2e,f lead to the pentacyclic cyclopropane systems 4a,b, azides 5 and 6, norderivative 9 and, by a base-corresponding induced elimination, dihydropyridine 10, a precursor of the zwitterionic alkaloids flavopereirine and 6,7-dihydroflavo-pereirine.