Addition reactions of heterocyclic compounds. Part LVI. Formation of 1,2-dihydroazocines from 1,2-dihydropyridines with dimethyl acetylenedicarboxylate

Abstract

1-Phenyl-(1), 1-phenyl-3-carbamoyl-(2), 1-methyl-3-cyano-(3), and 1-benzyl-4-methyl-1,2-dihydropyridine (4) with dimethyl acetylenedicarboxylate gave the corresponding dimethyl 1,2-dihydroazocine-6,7-dicarboxylates, a 1,2,4a,6a-tetrahydrocyclobuta[b]pyridine being detected as an intermediate in one case. N.m.r. variable temperature spectra gave evidence of ring flipping in the azocines but showed no valence tautomerism. The 3,4- and 5,6-double bonds of the azocines were reduced respectively by hydrogen over palladium and by sodium borohydride. Photolysis cyclised dimethyl 1,2-dihydro-1-phenylazocine-6,7-dicarboxylate (6) across the 3,6-positions to give the 1,2,4a,6a-tetrahydrocyclobuta[c]pyridine (17).