Regioselectivity and stereoselectivity of electrophilic quaternization of substituted 2-allyl(2-cyclohexen-1-yl)thionicotinic acids to thiazolo[3,2-a]pyridinium salts

The electrophilic quaternization of substituted 2-allyl(2-cyclohexen-1-yl)-thionicotinic acids proceeds regioselectively and stereoselectively as a trans process with the formation of salts of 4a,10a-cis-4,4a-trans-1,2,3,4,4a,10a-hexahydrobenzothiazolo-3,2-a]pyridinium acids. Trihalides of thiazolo3,2-a]-pyridinium acids exist in equilibrium with their betaine form. The formation of betaines and reactions that proceed with a change in the anionic part of thiazolo3,2-a]pyridinium salts have virtually no effect on the conformation of the heterocyclic cation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 256–263, February, 1990.