Cyclisation reactions of some 3-nitrosoimidazo[1,2-a]-pyridines and-pyrimidines. Ring-opening/ring-closure reactions with triethyl phosphite: reassignment by X-ray crystal structure and nuclear magnetic resonance

Abstract

Deoxygenation of 3-nitroso-2-phenylimidazo[1,2-a]-pyridines and -pyrimidines with triethyl phosphite does not lead to the products described in the literature as pyrido- and pyrimido-imidazoindoles (3) and (4), but to the open-chain derivatives, N-(2-pyridyl)- and N-(2-pyrimidyl)-benzimidoyl cyanides (5) and (6). X-Ray crystallographic analysis confirms the structure of (5a): orthorhombic system with a= 24.377 (6), b= 11.729 (3), c= 7.534 (2)Å, space group Pbca, Z= 8, d= 1.27 g/cm³, R= 0.061. Thermal ring-closure with triethyl phosphite of compounds (5) and (6) produced the 3-amino-2-phenylimidazo[1,2-a]-pyridines and -pyrimidines (8) and (9).