Addition reactions of heterocyclic compounds. Part XXIX. Cyclazines and quinolizines from stilbazole with dimethyl acetylenedicarboxylate, and their nuclear magnetic resonance spectra

Abstract

cis- and trans-Stilbazole with dimethyl acetylenedicarboxylate gave the tetramethyl 6-styryl-9aH-quinolizine-1,2,3,4-tetracarboxylates, which were isomerised to the 4H-isomers and to tetramethyl 1,2-dihydrocycl[3,3,2]-azine-2a,3,4,5-tetracarboxylate. Cyclazine formation was studied under various conditions. One of the methylene hydrogens of the cyclazine itself exchanged stereospecifically in boiling deuterioacetic acid. The nuclear magnetic resonance spectra of these compounds and the corresponding ethyl esters have been analysed. The 3-ester groups of the cyclazines are highly shielded by the 2-phenyl groups, and the 3-ethyl ester group appears as an ABX₃ system showing the asymmetric environment of the methylene group. Some reactions of these compounds are described.