A Concise and Efficient CuI-catalyzed Synthesis of Diimino Dihydroquinazoline Derivatives from Isocyanides and Guanidines Derivatives Through Intramolecular C-H Activation

A novel series of diimino dihydroquinazoline derivatives were synthesized from isocyanides and guanidine analogs in quantitative yields by applying an efficient, inexpensive, one-pot copper-catalyzed intramolecular C-H activation reaction under mild conditions. The structures were confirmed on the basis of IR, (HNMR)-H-1, C-13 NMR, mass spectral and elemental analysis data. The protocol offers advantages like short reaction time, a simple workup process, high yields, and an environmentally benign methodology. Interestingly, better results (yield = 82%) were observed in terms of the yield obtained by using a mixture of CuI, Cs2CO3 and acetonitrile as the catalyst, base, and solvent, respectively. The data also suggested that compound 5i is produced with the highest yield (87%) from the corresponding diisopropyl carbon diimide, 4-nitroaniline and phenyl isocyanide. Finally, a mechanistic explanation for the reaction promoted by cuprous iodide (CuI) was proposed on the basis of previous investigations and our experimental observations.