The mechanism of cycloaddn. of 1,4-dimethyl-2,3-dimethylenehexahydropyrazine to moderately and highly electrophilic alkenes is probed by stereochem. studies. Retention of configuration for the E/Z-isomeric alkenes fumaro- and maleonitrile and loss of stereospecificity for di-Me dicyanofumarate and di-Me dicyanomaleate show that the mechanism of cycloaddn. (concerted or stepwise) depends on the gap between nucleophilic and electrophilic character of the reaction partners. The behavior of 1,4-dimethyl-2,3-dimethylenenehexahydropyrazine follows that of other amino-substituted dienes.