Transition Metal-catalyzed Deoxygenative Reduction Of Phenols And Dehydrogenative Borylation Of Olefins

The selective deoxygenative reduction of 2,2’-biphenol has very considerable applications in organic synthesis,especially for the synthesis of ligands and heterocyclic compounds with a biphenyl skeleton.At present,the main methods for deoxygenative reduction of phenols include transition metal-catalyzed deoxygenative reduction,metal hydride-catalyzed deoxygenative reduction and electrochemical deoxygenative reduction.Currently,it is clear that many methods have been developed for transition metal-catalyzed functionalization and cross-coupling reactions of phenols and their derivatives through the cleavage of aryl C-O bonds.However,reductive defunctionalization via C-O bonds has not yet been totally explored.Therefore,it is very necessary to develop an efficient deoxygenative reduction method.In this background,we have achieved a palladium-catalyzed selective deoxygenative reduction of aryl triflate 2,2’-biphenol by using HCO₂H as a hydrogen source.It provides a new method for the deoxygenative reduction of aryl C-O bonds.The particular operation is as follows:Bisphenol is the research substrate for this study.Pd（OAc）₂,DPPF,Et₃N and HCO₂H are used as catalyst,ligand,base and hydrogen source respectively.The reaction is stirred at 80 ^oC or 120 ^oC for 15 hours.The advantages of the reaction:（1）Broad substrate scope;（2）High atom utilization;（3）Gram-scale synthesis;（4）Wide applications.Based on previous work and the study of our research group,alkenyl borate can efficiently construct carbon-carbon and carbon-heteroatom bonds.At present,the preparation methods of alkenyl borate mainly include hydroboration of alkynes,Miyaura boronization of alkenyl halides,and dehydrogenative borylation of alkenes.In general,dehydrogenative borylation of olefins is the best direct and effective method for constructing various substituted alkenyl boronic esters.According to the above hypotheses,we develop the rhodium-catalyzed1,4-dehydrogenative borylation reaction of conjugated diene derivatives.The operation of test is as follows:The reaction is based on conjugated diene derivatives using[Rh（cod）Cl]₂as the catalyst,Xantphos as the ligand,and n-octane as the solvent.In the presence of equivalent B₂pin₂and Norbornene（NBE）,it is stirred at 120 ^oC for21 hours.At present,we obtain the optimal reaction condition for1,4-dehydrogenative borylation product of conjugated diene derivatives.This paper is about the transition metal-catalyzed deoxygenative reduction of phenols and dehydrogenative borylation of olefins.Its chief contents include transition metal palladium-catalyzed selective deoxygenative reduction of2,2’-biphenol,product conversion and application research,and transition metal rhodium-catalyzed 1,4-dehydroboration of 1,3-diene and its outcome transformation.