Heterocyclic rearrangements. Part IV. Formation and reactions of some azepines

Abstract

Some 2,5-bridged tetrahydroazepines, where the bridging group X is NMe, N·CH₂Ph, or Se, have been prepared from 4H-azepines and also, when X is NH or Se, from (halogenomethyl)dihydropyridines byr ing expansion. When X is NH the product reacts further to give dihydroazepine and pyrrole derivatives. The stereochemistry of these bicyclic compounds, which varies little according to the bridging atom (including the case where X is S) has been elucidated, largely from n.m.r. measurements.

Ring contraction of the bridged azepine (X = S) with methyl iodide or bromide to a (halogenomethyl)dihydropyridine has been found to proceed through a dihydro-4-azepinyl sulphide and a 4H-azepine. The extreme lability of the 1,4-dihydro-4-iodomethylpyridine is demonstrated.

For ring expansion of 1,4-dihydro-4-(substitured methyl)pyridines, acetate cannot replace halide; a 4-acetoxy-1,4-dihydropyridine has given a dihydropyridine lactone when treated with ammonium hydroxide.