Formal Allylic C(sp~3)-H Alkylation Of α-alkylstyrenes By Rearrangement Of Intermediate Alkenyl Sulfonium Salts

Direct allylic C(sp~3)-H alkylation has become a valuable synthetic tool to forge C(sp~3)-C(sp~3)bond formation in organic synthesis,and has been widely applied in the synthesis of natural products,pharmaceuticals and other biologically active molecules.During the past decade,tremendous efforts have been devoted to transition-metal-catalyzed allylic C(sp~3)-H alkylation viaπ-ally-metal intermediates,leading to a linear type selective functionalization of terminal alkenes.In comparison,the branch selective C(sp~3)-H functionalization of terminal alkenes is very difficult to achieve.The readily installed alkenyl sulfonium salts have been investigated as promising coupling partners or building blocks for several decades.However,the most of the reported functionalization reactions are restricted to ipso-functionalization of alkenyl sulfonium salts by replacing the C-S bond.By comparison,the allylic C(sp~3)-H functionalization of vinyl sulfonium salts has received less attention.Herein,we expand this reactivity to the allylic C(sp~3)-H alkylation of branchedα-styryl sulfonium salts.With this method,a wide range of branchedα-styryl sulfonium salts were well tolerated,affording corresponding products in moderate to excellent yields.Notably,this method could also allow facile access to allylated carbon quaternary centers in a mild,metal-free manner.The specific contents are as follows:1.A new method was developed to improve the performance ofα-alkyl styrene is used as raw material to synthesize the intermediate alkenyl sulfonium salt,and then carry out the allylic C(sp~3)-H bond alkylation by rearrangement to finally obtain the target product.Then we studied the scope ofα-alkyl styrene tetrahydrothiophene sulfonium salts and had resulted in 21 target products.2.The variants of branchedα-alkyl styrene sulfonium salts were further investigated,and18 target products of various types were obtained in 58%-92%.3.The method was applied to the scale-up reaction,one-pot synthesis,and the late-stage functionalization of the bioactive molecule.All these indicate the potential application of this method in the field of organic synthesis.