Visible Light/Thermally-Promoted Synthesis Of Biphenols Derivatives

Biphenol derivatives are very important fine chemicals and have been widely used in natural products,pharmaceuticals,agrochemicals and functional materials,biphenol can also be used as organic small molecule catalysts and ligands.Traditional methods for synthesizing biphenols rely on transition metal catalysts or toxic strong oxidants,which does not meet the requirements for "green chemistry" and sustainable development due to their harsh conditions,difficulty in post-processing,unfriendly to the environment and heavy pollution.Therefore,it is of great significance to develop a green and efficient method for the synthesis of biphenol derivatives.In this paper,the biphenol derivatives were synthesized by visible light promotion or thermal promotion.(1)Visible light-driven di-t-butyl peroxide-promoted the oxidative homo-and cross-coupling of phenols are described.In the homo-coupling reaction,2,4-di-tertbutylphenol was selected as a model substrate to optimize the reaction conditions(photocatalyst,oxidant,solvent,wavelength and reaction time).The optimal reaction conditions were as follows: di-t-butyl peroxide as an oxidant(2 equiv.),dichloroethane as a solvent,at room temperature in nitrogen atmosphere under 6 × 3 W blue LEDs irradiation.Under the optimal reaction conditions,the desired product 2,2’-dihydroxy-3,3’,5,5’-tetra-tertbutylbiphenyl was formed in 85% yield.In the cross-coupling reaction,1,1,1,3,3,3-hexafluoro-2-propanol was found to be the best solvent,and the yields of the cross-coupling products are38%-72%.(2)Thermally-promoted synthesis of biphenol was also studied.In the homo-coupling reaction,2-tert-butyl-6-methyl-phenol was selected as a model substrate to optimize the reaction conditions(base,solvent,temperature,reaction time,etc.)The optimum reaction conditions were as follows: potassium carbonate as a base,air as an oxidant,water as a solvent,at 120 ℃ for 12 h.Under the optimal reaction conditions,2,2’-dimethyl-6,6’-di-tert-butyl-4,4’-biphenol was obtained in 70% yield.2,2’-dimethyl-6,6’-di-tert-butyl-4,4’-biphenol can be converted into 2,2’-dimethyl-4,4’-biphenol,which is a fine chemical with high added-value.