Tricyanovinylation of 2-aryl-1-vinylpyrroles: solvent- and substituent controlled chemo- and regioselectivity

2-Aryl-1-vinylpyrroles in acetone, THF and benzene react with tetracyanoethene chemo- and regiospecifically across the vinyl group to give 3-(2-arylpyrrol-1-yl)-1,1,2,2-cyclobutanetetracarbonitriles in 88-94% yield. The latter, upon recrystallization from EtOH, eliminates HCN and entirely rearranges to afford stereospecifically trans-(3E)-4-(2-arylpyrrol-1-yl)-1,3-butadiene-1,1,2-tricarbonitriles. In DMSO, along with the above [2+2]-cycloaddition, tricyanovinylation of the pyrrole ring occurs to form the corresponding 3- and 5-tricyanovinylpyrroles, the product ratio being dependent on the substituents in the pyrrole ring and the reaction conditions.