Polyphosphoric Acid Esters Promoted Synthesis of Quinazolin-4(3H)-imines from 2-Aminobenzonitrile

A novel method for the synthesis of quinazolin-4(3H)-imines (QIs) by trimethylsilyl polyphosphate (PPSE) promoted reaction of 2-aminobenzonitrile with secondary amides is reported. The reaction is general and allows for the synthesis of N3-aryl and N3-alkyl QIs with variable 2-substituents affording high yields. The procedure was extended to derivatives bearing additional functional groups. The method is operationally simple, involves easily available starting materials and a mild dehydrating agent, with wide functional group tolerance. The reaction procedure proved to be suitable for scaling-up. A possible reaction path via an intermediate nitrilium ion is proposed on the basis of literature data and experimental observations.