Heterocyclic compounds with bridgehead nitrogen atoms. Part 10. Synthesis in the pyrrolo[2,1,5-de]quinolizine series ([2.3.3]cyclazinones and [2.3.3]cyclazinylium salts) starting from quinolizines

Abstract

Ethyl 1-oxo-1H-pyrrplo[2,1,5-de]quinolizine-2-carboxylate was obtained by thermal cyclisation of di-ethyl quinolizin-4-ylidenemalonate and the corresponding 3-oxo-3H-1-carboxylate by reaction of 3-hydroxyquinolizinylium bromide with sodium carbonate and ethyl propynoate in boiling nitrobenzene. These isomeric esters were hydrolysed and decarboxylated to give 1H- and 3H-pyrrolo[2,1,5-de]quinolizin-1- and -3-ones and were converted into various pyrrolo[2,1,5-de]quinolizinylium salts, including the parent compound. The n.m.r. spectra and chemical properties of the pyrrolo[2,1,5-de]quinolizinylium ion are consistent, for the most part, with a structure in which the 1,2-bond is part of the aromatic system. Nucleophilic attack on this ion occurs at C-3 and, to a lesser extent, at C-5. Among the compounds obtained by such reactions was 5H-pyrrolo[2,1,5-de]quinolizin-5-one, thus leaving the corresponding 4-oxo-4H-compound as the only member of this isomeric series that remains unknown.