On the reaction of N-vinyliminophosphoranes. Part 16. A new synthesis of 5H-indeno[1,2-b]pyridines and 5H-indeno[1,2-b]pyridin-5-ones

Abstract

Thermal reaction of tributyl(inden-3-ylimino)phosphorane with α,β-unsaturated ketones and aldehydes led to a Michael-type C–C bond formation and subsequent aza-Wittig reaction to give 5H-indeno(1,2-b)pyridines in good to modest yield. The products were oxidized conveniently by chromium trioxide and t-butyl hydroperoxide to give 5H-indeno[1,2-b]pyridin-5-ones, including the 4-azafluorenone alkaloid onychine.