Effect of geminal substituents on dehydrogenation of dihydro derivatives of nitrogen heterocycles. 2,3-dihydroperimidines and benzimidazolines

A study was carried out on the rate of hydride ion displacement from 1,3-dimethyl-2-R-2,3-dihydroperimidines and 1,3-dimethyl-2-R-benzimidazolines to 1,3,5-trinitrobenzene. In all cases, inhibition by the substituents at C(₂) is observed but this effect is much more pronounced in 2,3-dihydroperimidines than in benzimidazolines. An x-ray diffraction structural analysis of 1,3-dimethyl-2-phenyl-2,3-dihydroperimidine showed that the geometry of 2,3-dihydroperimidines causes steric blocking of the hydrogen atom at C(₂) by the geminal substituent and substituents at the nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Saedinenii, No. 7, pp. 977–985, July, 1985.