Functionalization Reaction Of Alkyl Alcohols Via Alkoxy Radicals And Its Mechanistic Studies

Synthetic chemistry is of great significance in our daily life,providing essential materials for our human beings.With the progress of scientific and technological innovation,it is the common pursuit of all chemists to use green methods and simple raw materials for the synthesis of higher-value molecules.Given the wide availability of alcohols,direct modification and functionalization of alcohols is an appealing,valueadded transformations,which attracts a lot of synthetic chemists’ attention.In the past century,an array of classical reactions of alcohol have been developed including the nucleophilic substitution reactions,oxidation reactions etc.,which depend on the chemical properties of the lone pair electrons of the hydroxyl group.Over the last several decades,since radicals have been recognized as highly reactive intermediates that can accomplish diverse synthesis efficiently and concisely,functionalization of alcohol via alkoxy radicals generated by catalysis is considered to be a promising strategy for the synthesis and transformation of alkyl alcohols.In this thesis,the author presented several novel methods for the generation of alkoxy radicals,which could be successfully used to achieve various functionalization reactions of alkyl alcohol compounds.Details are as followings:1.The reaction activities of alkoxy radicals was investigated when silyl groups were introduced at the α-position of the hydroxyl group.The introduction of silyl groups changed the nature of the alkoxy radicals from 1,5-hydrogen transfer to 1,2-silyl transfer,producing a carbon radical at the α-position of the hydroxyl group.Experimental results demonstrated that,in the presence of more than one hydroxyl groups in the substrate,selective activation of the hydroxyl group connected to the same carbon atom as the silyl group could generate an alkoxyl radical.Additionally,this method was found to be compatible well with substrates involving multiple reactive sites,such as the C-H bond next to the oxygen atom,selectively producing the corresponding α-functionalized products in good yields.In terms of the mechanism,DFT calculations revealed that 1,2-silyl transfer was more favorable than 1,5-hydrogen transfer in both kinetics and thermodynamics.2.A versatile redox-neutral method for the ring-opening functionalization of cycloalkanols by electrophotochemical synergistic catalysis and using cerium as catalyst was developed.This approach allowed for cycloalkanols with different ring sizes to be cleaved while tolerating a broad range of functional groups.Notably,in the presence of chloride as a counteranion and electrolyte,this protocol selectively led to the formation of C-CN,C-C or C-S bonds instead of a C-Cl bond after β-scission.A preliminary mechanistic investigation indicated that the redox-active Ce catalyst could be tuned by electro-oxidation and photo-reduction,thus avoiding the use of an external oxidant.Spectroscopic characterizations(cyclic voltammetry,UV-vis,electron paramagnetic resonance,and X-ray absorption fine structure)suggested a Ce(III)/Ce(IV)catalytic pathway for this transformation involving Ce(IV)OR species.3.A method for the far-end desaturation of long-chain alkyl alcohols was developed by using cobaloxime as a hydrogen atom transfer reagent under electrophotochemical conditions.In this reaction,the substrate N-alkoxypyridinium salt and the cobaloxime catalyst were simultaneously reduced at the cathode,yielding alkoxy radicals and cobalt(II).These species then react to form an intermediate alkylCo(III)complex.Then,alkyl-Co(III)intermediate underwent photoinduced homolytic cleavage of the Co-C bond followed by β-H abstraction by Co(II)to furnish a Co(III)hydride and the desired alkene.Additionally,we found that various types of substrates were also well-tolerated in this reaction.