Study On The Dehydrogenative Cross-Coupling Reactions Of Alkenes Via Dual Photoredox And Cobalt Catalysis

Visible light photoredox catalysis has received continuous attention from chemists as a novel activation mode to activate organic small molecules into highly reactive radicals under mild conditions.Combining photocatalysis with metallic cobalt catalysis with unique properties to form a synergistic photo/cobalt dual-catalysis in dehydrogenative cross-coupling reaction is worth exploring and looking forward to.In this thesis,the photo/cobalt dual catalysis is combined with other novel and efficient substrate activation strategies to realize the dehydrogenative cross-coupling reactions of alkenes with alcohols and polyfluoroalkyl halides,respectively,which mainly include the following:（1）Proton-coupled electron transfer（PCET）-involved ring-opening alkenylation of cyclic alcohols via dual photoredox and cobalt catalysisAlcohols are one of the abundant classes of compounds in nature and an important source for obtaining alkyl groups,which are difficult to be applied in radical chemistry due to their ultra-high redox potentials and C-O and O-H bonding energies,while alkenes are common radical acceptors in photopromoted organic synthesis.In this thesis,a series of unsaturated ketone compounds were synthesized by combining photo/cobalt dual catalysis with a proton-coupled electron transfer activation strategy to achieve ring-opening alkenylation of cycloalcohols with alkenes,and a series of intramolecular ring-opening and then ring-closing ring-expansion reactions were attempted.The activation of aryl radical cations with base synergistic with hydroxyl groups of alcohols through the PCET process was demonstrated by comparison of substrate control experiments with ¹H NMR spectra of the mixtures.Radical capture experiments also demonstrated the presence of key intermediates in the reaction process.Fluorescence quenching experiments and cyclic voltammetry experiments explain well the poor reactivity of the quenching pathway of the excited state photocatalyst with electron-rich alkenes.（2）Multifluoroalkylation of alkenes by photo/cobalt and halogen atom transfer tricatalysisThe physical and adsorption,distribution,metabolic and excretory properties of organic compounds containing fluorine elements are inextricably linked to them,and the selective introduction of difluoromethylene（CF₂）at specific positions in organic molecules can significantly improve the metabolic stability and oral bioavailability of bioactive molecules.In this thesis,the polyfluoroalkylation of alkenes was achieved by photo/cobalt and halogen atom transfer tricatalysis using cheap and readily available ethyl bromodifluoroacetate as a fluorine source and alkenes as radical acceptors.Photoredox-catalyzed coupling reactions of alkenes with halogenated hydrocarbons are usually dominated by atom transfer radical addition（ATRA）processes to obtain kinetically advantageous bifunctionalized products of alkenes,and direct C（sp²）-H bonded polyfluorinated alkylation products of alkenes can be obtained by this strategy.