Theoretical Study For Rh-catalyzed C-h Bond Activation Cyclization And Experimental Exploration For Co-Catalyzed Reduction Etherification

In this paper,transition metal cobalt-catalyzed reductive etherification of alcohols with ketones and aldehydes has been studied experimentally and DFT calculation was employed to study the mechanism of transition metal rhodium-catalyzed C-H bond activation and cyclization.Transition metal rhodium-catalyzed C-H bond activation cyclization is an efficient method to construct fused ring compounds,so it is necessary to study the mechanism of reaction.With the rapid development of theoretical computational chemistry,it plays an important role in explaining the principle of experimental reaction and predicting the activity of reaction.Based on this,we studied the mechanism of Rh(III)-catalyzed C-H/N-H[4+2]cyclization coupling reaction by using density functional theory.Theoretical calculations indicated that the mechanism of Rh(III)-catalyzed[4+2]annulation of benzamide and vinylene carbonate reaction including:the insertion of vinylene carbonate into Rh-C bond,intramolecular 1,2-Rh-C bond migration assisted decarboxylation process,deprotonation under carbonic acid assistance,C-H/N-H activation to regenerate rhodacycle active species.In addition,we propose a new activation mode of vinyl carbonate in transition metal catalyzed coupling reaction.Ether compounds are widely used in the industrial production of aromatics,lubricants and surfactants.Transition metal catalyzed reductive etherification of alcohols with ketones and aldehydes can efficiently and rapidly construct ether compounds.The traditional reduction etherification reaction mostly use precious metals(palladium,ruthenium)as catalyst,organosilicon species as reducing agent and strong acid system,which leads to the limitation of its synthesis and application,so it is necessary to develop environmentally friendly reactions with high atom utilization.In view of the above scientific problems,we mainly studied cheap metal cobalt catalyzed the reduction etherification of alcohols with ketones and aldehydes.Specific contents include:1)With the help of In(OTf)₃ and H₂ as reducing agent,triphos-Co(II)can effectively catalyzed this reaction.2)The reaction has good functional compatibility and can catalyzed the reaction of different kinds of aromatic aldehydes/ketones and different alcohols.In addition,the electronic effect and steric effect of the benzene ring have no obvious effect to the catalytic efficiency of the reaction.3)The exploration of mechanism shows that triphos-Co(II)has the ability to split hydrogen and form[Co]-H species.Then,acetophenone can be reduced to1-phenylethanol through[Co]-H specie.Under the catalysis of lewis acid,1-phenylethanol and benzyl alcohol can further transfom to the ether compound through dehydration condensation process.In addition,acetophenone can react with benzyl alcohol to form hemiacetal intermediate,then the hemiacetal intermediate was selectively hydrogenated by[Co]-H species to produce the target product and1-phenylethanol.Finally,1-phenylethanol reacted with benzyl alcohol to form ether through the catalysis of Lewis acid.