Cycloaddition of 1,4-Dimethyl-2,3-dimethylenehexahydropyrazine to Electron Deficient Alkenes

The mechanism of cycloaddition of 1,4-dimethyl-2,3-dimethylenehexahydropyrazine to moderately and highly electrophilic alkenes is probed by stereochemical studies. Retention of configuration for the E/Z-isomeric alkenes fumaro- and maleonitrile and loss of stereospecificity for dimethyl dicyanofumarate and dimethyl dicyanomaleate show that the mechanism of cycloaddition (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.