Studies On Iron-catalyzed Alkynylation Of Methane And Other Light Alkanes By Photocatalysis

Substituted alkynes are fundamental structural motifs and important building blocks in the synthesis of antibiotics,antimycotics,polymers,optical or electronic materials,and liquid crystals.Their synthesis has attracted much attention throughout the history of organic chemistry.In addition,light alkanes are major constituents of petroleum and natural gas,and widely distributed in nature.Due to their high hydrocarbon bond energy,intrinsic inertness and poor solubility of gaseous light alkanes,C（sp³）–H activation of light alkanes,regarded as one of the“holy grails”in synthetic chemistry,has met great difficulty.Compared to traditional C（sp³）–H activation processes,photoinduced hydrogen atom transfer（HAT）processes exhibit several advantages including mild conditions and good regioselectivity,thus achieving big progress recently.According to the demand by atom-economic and sustainable chemistry,direct C（sp³）–H alkynylation of alkanes through photoinduced HAT processes without pre-functionalization processes represents an appealing strategy for synthesis of valuable internal alkynes.Depending on this strategy,this dissertation obtained some achievements shown as follows:We have developed an efficient,green,and highly selective method for direct alkynylation of light alkanes including methane by iron photocatalysis.With Fe Cl₃·6H₂O as photocatalyst,aryl alkyne sulfones as alkynylation reagents,and alkynylation reaction of cyclohexane as model reaction.Cyclic and linear alkanes,including methane,ethane,and heavier gaseous alkanes,can efficiently achieve their alkynyl processes with significant regioselectivities on 1°and 2°C（sp³）–H.A variety of phenyl ethynyl sulfones were also applied as substrates,presenting high yields and efficiency.The novel method realized 35 examples in total on synthesis of internal alkynes with good tolerance on diverse functional groups including naturally-sourced fragments.Investigations on the reaction mechanism showed photo-induced ligand-to-metal charge transfer（LMCT）of Fe–Cl complexes instead of traditional photosensitizer could generate chlorine radicals,which could act as active HAT catalysts to activate aliphatic C–H bonds.Consequently,aryl ethynyl sulfones trapped the corresponding alkyl radicals and realized direct alkynylation of light alkanes.This method can effectively realize the conversion process of natural alkanes to high value-added products mediated by chlorine radicals,providing convenience for synthesis of intrinsic alkynes.We believe this strategy will have wide application and applied prospects.