Easy access to medium rings by entropy/strain reduction. Part 2. The ready availability of cis,cis-2,4-diene-1,6-diols and derived dibromides allows a simple and mild route to substituted 2,7-dihydro-1H-azepines

Abstract

Hydride reduction of a series of substituted cis,cis-2,4-diene-1,6-dioates 1 provided the corresponding 1,6-diols 2, most of which were converted to the 1,6-dibromides 3 with phosphorus tribromide. Reaction of a selection of these dibromides with primary alkylamines in the presence of sodium hydrogen carbonate provided a simple and mild synthesis of substituted dihydroazepines 4. The cleanest products were obtained with toluene-p-sulfonamide as the nitrogen source. Bis(dihydroazepines) 5 were also synthesised from diamines while hydrazine yielded a hydrazinium salt 6. Aniline could be induced to take part in the reaction in the presence of butyllithium furnishing a low yield of N-phenyldihydroazepines 8.