Synthesis of 2,4-Diaminoquinazolines and Tricyclic Quinazolines by Cascade Reductive Cyclization of Methyl N-Cyano-2-nitrobenzimidates

An efficient route to N4-substituted 2,4-diaminoquinazolines has been developed by employing tandem condensation of cyanoimidate–amine and reductive cyclization in iron–HCl system. This method is tolerant of a following intramolecular N-alkylation and produces two fused heterocycles in a one-pot procedure. This protocol is a facile two-step synthesis of tricyclic quinazolines, which is effected by potent cyanoimidation and tandem reductive cyclization from 2-nitrobenzaldehydes. Moreover, the forming process of tricyclic quinazolines has been investigated from the ring-opening/ring-closing cascade point of view. It is found that the preparation of tricyclic quinazolinones in good yields relies on the selective hydrolysis of tricyclic quinazolines in base or acid system.