Dehydrogenation of Hantzsch esters: abnormal course of reaction of the 4-p-dimethylaminophenyl derivative

Reactions of diethyl 4-p-dimethylaminophenyl-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate with various electrophiles, X+, give diethyl 2,6-dimethylpyridine-3,5-dicarboxylate and compounds which include the ipso substitution products, p-C6H4X·NMe2.