Metal‐Free, Photoredox‐Catalyzed Synthesis of Quinazolin‐4(3H)‐ones and Benzo[4,5]imidazo[1,2‐c]quinazolines Using Trialkylamines as Alkyl Synthon

Abstract Highly functionalized quinazolin‐4(3 H )‐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(1 H )‐one ( 3’ ) in the photocatalytic cycle to afford the 2,3‐disubstituted‐quinazolin‐4(3 H )‐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.