Ts. Kim et al., ON THE LONG-STANDING QUESTION OF AN ET OR POLAR MECHANISM FOR THE CYCLOADDITION OF TETRACYANOETHYLENE WITH ELECTRON-RICH ALKENES, Perkin transactions. 2, (3), 1995, pp. 577-580
An ET mechanism is decisively excluded for the zwitterionic cycloaddit
ion of tetracyanoethylene and bis(4-methoxycinnamyl) ether. A polar me
chanism for this and analogous zwitterionic cycloadditions is therefor
e strongly indicated.