Synthesis of 5-oxo-1,2,3,5,6,7-hexahydroimidazo-[1,2-a]pyridine-8-carbonitriles, 6-oxo-2,3,4,6,7,8-hexahydro-1H-pyrido[1,2-a]pyrimidine-9-carbonitriles, and 7-oxo-1,2,3,4,5,7,8,9-octahydropyrido[1,2-a][1,3]diazepine-10-carbonitriles

A simple method for the synthesis of the title compounds is described. Thus, α,β-unsaturated esters (1) are transformed in the already described 2-methoxy-6-oxo-1,4,5,6-tetrahydropyridine-3-carbonitriles (3) which are treated with NH₂(CH₂)_nNH₂ (n = 2, 3, 4) to afford the corresponding bicyclic compounds (4, 5, and 6). The nitrogen bridged nature of these compounds is determined by an X-ray structure analysis of 4b. A ring opening-ring closure mechanism is proposed for the formation of structures (4-6) on the basis of the reaction between 3b and ¹⁵N,¹⁵N′-ethylenediamine which afforded ¹⁵N,¹⁵N′-4b.