Reaction of phenyl radicals with dialkyl azodiformates: formation of, and nuclear magnetic resonance studies of conformational restrictions in, tetra-alkyl 1,4-diphenyltetra-azane-1,2,3,4-tetracarboxylates

Abstract

Dialkyl azodiformates (RO₂C·NN·CO₂R; R = Me, Et, or Bu^t) do not undergo annelation reactions with phenyl radicals from benzoyl peroxide, to give tetrahydrobenzotetrazines. Instead they give good yields (up to 69%) of the novel, very stable tetra-alkyl 1,4-diphenyltetra-azane-1,2,3,4-tetracarboxylates (4), formed by addition of phenyl radicals to give hydrazyls PhN(CO₂R)·N(CO₂R)· which then dimerise. Reaction of dimethyl azodiformate with triphenyl(phenylazo)methane gives dimethyl N-phenyl-N′-triphenylmethylhydrazodiformate (9; R = Me). Variable-temperature n.m.r. studies of the latter and of the tetra-azanes (4) show that considerable barriers to rotation about N–CO₂Et bonds exist in these compounds.

Oxidation of diethyl N-phenylhydrazodiformate (10) by lead tetra-acetate does not give the tetra-azane (4; R = Et) but instead proceeds via a novel deformylation to give ethyl phenylazoformate (PhNNCO₂Et).