N-Iodo-amides: mechanism of intramolecular reactions with aromatic rings of amido-radicals in Σ- and Π-electronic states

Abstract

Intramolecular cyclisations of amido-radicals generated by homolysis of N-iodo-amides onto aromatic systems gives γ- and δ-lactams, in cases where the aromatic rings can rotate, and only δ-lactams in rigid planar systems. Kinetic studies of the cyclisation of N-methylbiphenyl-2-carboxamide with t-butyl hypoiodite under irradiation have shown that γ- and δ-cyclisation products are formed in parallel and that the reactions have different activation energies and entropies. Reactions of N-methyl derivatives of 1,2,3,4-tetrahydro- and 1,2-dihydro-phenanthrene-4-carboxamides with t-butyl hypoiodite under irradiation have provided evidence that Π-conjugation is a prerequisite for δ-lactam formation. From a consideration of the molecular orbitals involved it is suggested that γ- and δ-cyclisation reactions occur with amidyls in the Σ- and Π-electronic states.