Transition Metal-free Visible Light-driven Photoredox Oxidative Annulation Of Arylamidines

Quinazolines are classes of fused heterocycles that are of considerable interest because of the diverse range of their biological properties,for example,anti-lung cancer,?-adrenergic blocker.Because of the wide demand for substituted quinazolines,many synthetic strategies have been developed.According to literatures,we find that until now most of the strategies all require the use of either strongly acidic or basic conditions,and/or the preparation of activated intermediates.So developing a green,safe and efficient methodology for the functionalization of quinazolines is necessary.Recently,we developed a C-H oxidative functionalization and N-acyliminium cyclization for the synthesis of ?-halo-pyrrolidinones and pyrrolones.Herein we report a method for the synthesis of quinazolines through the versatile metal-free oxidative C(sp3)-C(sp2)bond-forming under photoredox conditions.Features of this reaction include: 1)Dehydrogenation coupling reaction was complete under photoredox conditions;2)using organic photocatalyst Rose Bengal as the catalyst which make the methodology economic and environmentally friendly;3)synthesizing a series of quinazolines derivatives;4)generating new C(sp3)-C(sp2)bond.We choose a variety of substituted N-benzyl-N'-phenyl benzimidamides as substrates,1 mol% organic photocatalyst Rose Bengal as the catalyst,CBr4 as the oxidant,potassium carbonate as base,using a 18 W fluorescent lamp as the visible light source and 24 quinazoline derivatives with potential pharmacological activities have been synthesized in DMSO under heating.All the compounds have been well characterized by 1H NMR,13 C NMR,LR-MS and HR-MS.A plausible mechanism of the reaction process has been proposed.Our proposed mechanism well explained the reasons for the bromide byproducts generated,and the addition of 1 mol % photocatalyst on the byproduct inhibition.