Dehydrogenation of secondary formamides

Abstract

N-Diphenylmethyl-(1a), N-cyclohexyl-(1c), N-triphenylmethyl-(1d), and N-phenyl-formamide (1e) have been dehydrogenated to give the corresponding isocyanates (2) by treatment with diethyl azodicarboxylate (52–60% yields) or with palladium (8–37% yields). N-Benzylformamide (1b) gave only traces of benzyl isocyanate under both these conditions. N-Diphenylmethylformamide (1a) was also dehydrogenated to give N-formyl-diphenylmethanimine (3a), which dissociated to give benzophenone: N-benzylformimide similarly gave benzaldehyde. The formamides were also decarbonylated by palladium to give amines, and these reacted in situ with the corresponding isocyanate: in this way the formamide (1a) gave NN′-bisdiphenylmethylurea (16), (1c) gave NN′-dicyclohexylurea (17), and (1e) gave NN′-diphenylurea (5e). Other products were obtained: (1c) gave NN′-dicyclohexylformamidine (18), (1d) gave triphenylmethane, isocyanic acid, benzophenone, and triphenylmethanol, and (1e) gave oxanilide (19).

Thermolysis of the neat formamides (1a) and (1d) at >220° gave the same products as obtained in the catalysed reactions.