Study On The Silver-Catalyzed Intermolecular C-H Insertion Reaction Between Sulfonylhydrazone And Alkanes

It is a bottleneck problem for the petrochemical industry to achieve a major breakthrough to selectively activate the C-H bond of saturated alkanes to construct C-C and C-X bonds under mild conditions.The C(sp~3)-H bond energy is high and the difference between them is very small.Therefore,the direct functionalization of C-H bond of alkanes,especially the formation of C-C bond,has double challenges of activity and selectivity,which is the most challenging topic at present.The alkylation of C(sp~3)-H bond induced by carbene is a new and promising strategy for the construction of alkyl-alkyl bond.For example,Professor Davies of Emory University recently reported the use of chiral donor-acceptor rhodium carbene to perform a series of regioselective,diastereoselective and even enantioselective functionalization of C(sp~3)-H bonds of unactivated 1~o,2~o,and 3~oC-H bonds in simple alkanes.Pérez and Dias have developed a series of acceptor carbene and alkane C-H bond insertion reactions catalyzed by copper and silver.However,up to now,EWG stable diazo compounds have been used as carbene precursors,because EWG can significantly improve the electrophilicity of metal carbene.The product must also contain EWG,which to some extent limits the diversity of its products and hinders its further application in organic synthesis.Benzoylhydrazone has been widely studied as a donor carbene precursor,but it has not been applied to the C-H functionalization of alkanes.There are only sporadic intramolecular reactions,and it is limited to the C(sp~3)-H bond activated by heteroatoms.The following challenges exist in the intermolecular reactions:(1)the donor group weakens the donor type carbene electrophilicity and has low reactivity to C-H bond;(2)the donor type diazo compound is unstable and prone to self coupling reaction;(3)the product benzyl C-H bond is more active and prone to over insertion.Tp~xAg is a weak coordination nitrogen scorpion complex,which contains three pyrazole rings.It can improve the electrophilicity of silver carbene intermediates by adjusting the electrical properties of the substituents on pyrazole,reducing the?-feedback effect of silver center on carbene carbon,so as to improve the C-H bond reactivity of donor carbene.In this paper,o-trifluoromethyl phenylsulfonylhydrazone developed by our research group is used as a mild donor diazo precursor to realize the C-H bond benzylation of phenylsulfonylhydrazone and cycloalkanes under the catalysis of Tp~xAg.For the first time,the insertion of nonactivated C(sp~3)-H bond by donor carbene was realized.This reaction has the advantages of high yield,wide range of substrates,simple operation and no need to use peristaltic pump drop.It can realize gram scale synthesis in the laboratory,thus providing a general practical method for the synthesis of alkylaromatics from phenylsulfonylhydrazone and cycloalkane.