Manganese-catalyzed Coupling Reaction Of Alcohols Based On Dehydrogenative Strategy

Transition metal-catalyzed dehydrogenative coupling reaction is highly atom economical and environmentally friendly,since it typically produces water or hydrogen gas as the by-products,and the methodology has been proved as an efficient method for the formation of carbon-carbon bonds and carbon-hetero bonds.On the other hand,alcohols can be obtained from biomass,which is widespread in nature.The dehydrogenative coupling reaction using alcohols as the starting material can realize the sustainable transformation of alcohols into value-added compounds.In recent years,the replacement of noble metal catalysts by non-noble metal catalysts,which is earth-abundant and less toxic,has become a trend in catalysis.In this thesis,we synthesize a range of pincer manganesebase complex and develop the cross coupling reaction of secondary alcohols,primary alcohols and methanol via hydrogen borrowing strategy,as well as synthesis of carbamates and ureas by acceptorless dehydrogenative coupling reaction of formamide and alcohol(amine)is described.Part one: Multi-component reaction(MCR)is one of the most effective tools for the construction of complex molecules,which can avoid the tedious separation and purification process of intermediates,the main challenge of the method is the control of reaction selectivity.Herein,We regulate the rate of hydrogen borrowing coupling reaction between different alcohols by pincer manganese catalyst and realize chemselective hydrogen borrowing coupling of secondary alcohols,primary alcohols and methanol.The catalytic system demonstrates a broad substrate scope and synthesizes a series of β,β-methylated/alkylated secondary alcohols in medium to good yields.Mechanistic investigations suggest that the process initiates by dehydrogenation of the primary alcohol and secondary alcohol with manganese-base catalyst results in ketone and aldehyde.Subsequently,the ketone and aldehyde undergo aldol condensation/dehydration/catalytic hydrogenation to generate the benzylated secondary alcohol as a key intermediate.Finally,the product is obtained by a similar hydrogen borrowing coupling process between the benzylated secondary alcohol and methanol.Part two: Carbamates and ureas are widely existed in pharmaceuticals,pesticides and functional materials,The traditional synthetic methods usually rely on phosgene or isocyanate,which is unfriendly to environment and human.So the use of readily available and safe materials to synthesize carbamate and urea is highly desirable.By surrogating isocyanate with formamide precursors,we developed an approach to access multiple carbamates and ureas via manganese-based pincer complex catalyzed acceptorless dehydrogenative coupling reactions.We speculate that intermediate isocyanate is generated by dehydrogenation of formamide,and then the intermediate reacts with alcohol(amine)to complete the transformation.