Metal‐Free, Photoredox‐Catalyzed Synthesis of Quinazolin‐4(3H)‐ones and Benzo[4,5]imidazo[1,2‐c]quinazolines 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. A metal‐free, visible‐light photocatalytic approach for the construction of 2‐alkyl substituted quinazolin‐4(3H)‐ones and benzo[4,5]imidazo[1,2‐c]quinazolines using trialkylamines as carbon synthons has been developed. Some of the notable features of this methodology include the synthesis of potent central nervous system depressants (CNS) drug molecules methaqualone (3 la), mecloqualone (3 pa) and gram‐scale synthesis.