Effect of solvent nature on the regioselectivity of the reactions of pyridinium ylides with E-1,2-di(alkylsulfonyl)-1,2-dichloroethene. From the reaction of 1,3-dipolar cycloaddition to the reaction of nucleophilic addition–elimination (AdN–E1,5)

The effect of solvent nature on the reactions of pyridinium ylides with E-1,2-di(alkylsulfonyl)-1,2-dichloroethene was investigated for the first time. It was found, that in aprotic solvents (CHCl3, DMF, CH3CN) these reactions take place as a 1,3-dipolar cycloaddition (1,3-DC) followed by double elimination with the formation of substituted 1,2-di(alkylsulfonyl)indolizines. In a protic solvent (EtOH) in the presence of excess Et3N and heating, the reactions of substituted pyridinium salts with E-1,2-di(alkylsulfonyl)-1,2-dichloroethenes take place simultaneously as a 1,3-DC and as an addition–elimination (AdN–E1,5) and lead to the formation of 1,2-di(alkylsulfonyl)indolizines and 4,5-di(alkylsulfonyl)furans.