Reactions of 1,1-bis(N,N-dimethylamino)-1,3-butadiene with olefins. Zwitterion formation and (4+2) cycloaddition as competing pathways

Article abstract of DOI:10.1016/0040-4039(90)80202-W

Reactions of 1,1 bis (N,N-dimethylamino)-1,3-butadiene (2) with acrylonitrile and tetracyanoethylene are described. At 80°C acrylonitrile affords a (4+2) cycloadduct (3), whereas a zwitterion (4), formed from 2 and tetracyanoethylene even at -40°C, is characterized in solution and trapped as picrate. It eliminates hydrogen cyanide at T > -20°C to give a cyanine (5). Ring closure of the zwitterion either to a (2+2) or to a (4+2) cycloaduct is not observed.