Utility of sec-Mannich bases of cycloalkanones in synthesis of mixed Mannich bases and fused heterocycles with ring junction nitrogen atom

Treatment of cycloalkanones 1a-c with benzalaniline or dibenzal-p-phenylenediamine gave the corresponding cycloalkanone sec-Mannich bases 2a-c and 4.Whereas, the reaction of 1a or b with benzal-1-naphthylamine afforded the condensed systems 7 and 8. 2,6-di(p-anisal)cyclohexanone (10) was obtained from 1b and N, N'-bis(p-anisal)ethylenediamine 9.On the other hand, treatment of the bis-(Mannich base) 12 with benzalaniline gave the mixed Mannich base 13. The tetra-base 14 was obtained by treating 2b with ammonium chloride and formaldehyde, or from the tris-(Mannich base) 15 and benzalaniline. Schmidt reaction of 2a-c and 4 gave N-phenyl-α-aminobenzyl derivatives of piperidin-2-one 16, azepan-2-one 17, azocan-2-one 18 and the bis-(azepan-2-one) derivative 19, respectively. The potential of compounds 16 and 17 as precursors to fused heterocycles containing a nitrogen atom at a ring-junction was investigated. The 1,2,4-triazepine derivatives 25 and 26 were obtained by treating 2a,b with hydrazine and formaldehyde.