Oxidative coupling and unusual hydroxymethylation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the presence of dicyanomethane

Potassium permanganate oxidizes a mixture of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (THP) 1 and dicyanomethane to 2-dicyanomethylidenetetrahydropyridine 2, but using manganese dioxide leads to the unusual oxidative hydroxymethylation of 1; subsequent treatment of the 3-hydroxymethyltetrahydropyridine 4 formed with aqueous potassium permanganate results in lactamination, accompanied by aromatization or oxodihydroxylation.