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Paper | Regular issue | Vol 32, No. 6, 1991, pp.1063-1079
Published online, 1st January, 1970
DOI: 10.3987/COM-90-5512
Heterocycles from Nitrile Imines. Part III. Substituent Effect on Ring-Chain Tautomerism of 1,2,3,4-Tetrahydro-s-tetrazines

Mustafa M. El-Abadelah,* Ahmad Q. Hussein, and Haythem A. Saadeh

*Chemistry Department, Faculty of Science, University of Jordan, Amman 11942, Jordan

Abstract

Selected series of 6-substituted 4-aryl-3-heteroaryl-1-methyl-1,2,3,4-tetrahydro-s-tetrazines (V:1-12) were synthesized via direct interaction between appropriate nitrile imine and model methylhydrazones. The extent of "ring-chain" tautomerism, as evidenced from nmr spectral data of V, is dependent on the nature of substituents at N-4, C-3, and C-6. The results reveal that: (i) The concentration of the cyclic tautomer tends to decrease as the basicity of the arylated N-4 decreases. (ii) For C-3 substituents, the cyclic tautomer ratio decreases in the order: phenyl>pyridyl>furyl>thienyl. (iii) For C-6 substituents, the cyclic ratio decreases in the order: C6H5>CO2Me>COMe. These trends are interpreted in terms of conjugative and electronic effects.