Carboxylation Of Styrenes With CBr₄ And DMSO Via Cooperative Photoredox And Cobalt Catalysis

?,?-unsaturated carboxylic acid and its derivatives is an important organic raw materials and pharmaceutical intermediates,is widely used in chemical,food,medical,spices,feed and other fields.The directly carboxylation of alkenes is a formidable challenge despite its high potential as a practical method for the preparation of unsaturated carboxylic acid derivatives.A well-known process for carboxylation of alkenes is the transition-metal-catalyzed C–C bond formation with CO₂,which has become a fundamental synthetic transformation in recent years.Most of those methodologies require the use of rare and expensive metals and can not be used for terminal olefins.The visible-light driven photoredox catalyzed radical-mediated approach can be a complementary route to the carboxylation of alkenes because radicals have high activity and efficiency and solar energy?visible light?is clean,green and renewable.We herein report the successful development of a carboxylation of styrenes employing CBr₄ and DMSO via cooperative photoredox and cobalt catalysis.CBr₄ serves as the carbon source and DMSO serves as the oxidant,oxygen source and solvent under these photocatalytic conditions.The reaction has the following characteristics:1)using cheap and green dye as the photocatalyst;2)mild reaction conditions at 50°C;3)using solvent dimethyl sulfoxide as the oxidant which is more environmentally friendly and efficient.We synthesized of more than 20?,?-unsaturated carboxylic acids employing CBr₄and olefins using eosin Y disodium and Co I₂ as cooperative catalyst at 50 ^oC,DMSO serves as solvent and oxidant.All compounds synthesized have been confirmed by ¹H NMR,¹³C NMR,MS and HR-MS.To confirm the mechanism,¹⁸O-labeled H₂O and DMSO experiments were performed under optimized conditions.These experimental results indicated that DMSO served as the source of oxygen in this transformation.We also conducted a series of control experiments to prove the mechanism.