Metal‐Free, Photoredox‐Catalyzed Synthesis of Quinazolin‐4(3H)‐ones and Benzoimidazoquinazolines Using Trialkylamines as Alkyl Synthon

Highly functionalized quinazolin‐4(3H)‐ones were synthesized from reactions of N‐aryl‐2‐aminobenzamides with trialkylamines under photocatalytic conditions by using eosin Y (EY) as a catalyst. The reaction proceeds under mild conditions in aqueous acetonitrile and has a broad substrate scope. Mechanistic studies disclosed the electron‐donor nature of the intermediate 2,3‐dihydroquinazolin‐4(1H)‐one (3’) in the photocatalytic cycle to afford the 2,3‐disubstituted‐quinazolin‐4(3H)‐ones (3). This methodology has been extended to synthesize benzo [4,5] imidazole[1,2‐c] quinazolines and 3 aa on a large scale. Furthermore, the synthesis of potent central nervous system depressant (CNS) drug molecules such as methaqualone (3 la) and mecloqualone (3 pa) was also achieved successfully.