Light-Mediated Aliphatic C-H Functionalization Via Hydrogen Atom Transfer

Hydrogen atom transfer(HAT),a kinetic process of concerted electron and proton transfer from a hydrogen donor to an acceptor,has been proved to be a direct and efficient method for generating radicals.In recent years,light-promoted hydrogen atom transfer catalysis has been developed as a hot topic in synthetic organic chemistry.With the use of clean and easily available light energy,aliphatic C-H bonds can be easily activated to generate highly active free radical intermediates for the efficient access of complex molecules from cheap and easily available chemical feedstocks.In this thesis,light-promoted aliphatic C-H functionalization based on hydrogen atom transfer using various functionalization reagents are studied,and three parts of work are mainly included.A robust and practical FeCl3/HCl photocatalytic system is identified,enabling efficient C-H alkylation,oxidation,chlorination,fluorination,amination,alkynylation,and sulfonylation with total turnover number(TON)of up to 9,900.Using mechanistic studies and TD-DFT calculations,the aliphatic C-H activation is supposed to be mediated by chlorine radical,in situ generated from a photoactive tetrahedral[FeⅢCl4]via ligand-to-metal charge transfer excitation.Using the combined catalysis of tetrabuty lammonium decatungstate(TB ADT)and chiral spiro phosphoric acid,a light-mediated asymmetric C-H functionalization of aliphatic hydrocarbons with exocyclic enones has been established.By the screening of chiral phosphoric acids,a variety of cycloalkanes,benzylic,and allylic hydrocarbons can be converted to enantioenriched chiral cyclic ketones.This protocol is supposed to proceed via a hydrogen atom transfer/radical addition/hydrogen abstraction/enantioselective protonation relay process.Using TBADT as a HAT catalyst and chiral spiro phosphoric acid as chiral protontransfer shuttle(CPTS),an asymmetric photocatalytic C(sp3)-H bond addition to αsubstituted acrylates is developed,generating a series of functionalized chiral α-amino acid derivatives in good to excellent yields.This method provides an economic and rapid approach for the construction of optically active compounds from basic chemical feedstocks.