Quinone Imine Route to Benzimidazol-2-ylcarbamates. Part 1. Synthesis of Open-chain and Cyclic 5-Acylamino Derivatives.
The synthesis of the N',N''-bismethoxycarbonyl-N-(4-acylaminophenyl)guanidines (4) and (7) is described.Oxidation of these with LTA has led to the benzimidazol-2-ylcarbamates. (8), (9) and (10) through a regiospecific cyclisation of quinone imine intermediates.If the acylamino group is part of a ring, the yield of benzimidazoles (15) increases with the size of the lactam ring.The direction of ring closure may be controlled by electronic and steric factors.