Auxiliary-assisted Palladium(?)-Catalyzed Direct C(sp~2)-H Silylation Of Acetophenone Derivatives

Organosilicon compounds play an important role in organic synthesis,materials science and pharmaceutical molecules due to their unique physical and chemical properties,which makes the synthesis of organosilicon compounds become the focus of scientists.Among these reported methods,the transition metal catalyzed C-H activation method stands out,and palladium catalyst has been widely used in the field of C-H activation.Although Pd catalyzed C-H silylation of benzamides,benzylamine,and benzylsulfonate has been achieved,it is necessary to extend the substrates to other types of aromatic compounds.Herein,in this paper,acetophenone was used as the substrate,and the Pd-catalyzed ortho-C-H silylation of acetophenone was successfully achieved with the aid of a directing group.Using directing group-masked acetophenone derivative as a substrate,and then the reaction conditions were screened.Indeed,the desired arylsilanes product were obtained under the condition of using oxime-4-Aminoheptafluorotoluene as directing group,Pd Cl₂(Me CN)₂ as catalyst,silver fluoride and copper trifluoroacetate as co-oxidants,lithium fluoride as base,and trifluorotoluene as solvent,heating at 100°C for 7 hours in an air atmosphere.With the optimum reaction conditions in hand,we surveyed the substrate scope.Substrates with different functional groups in the ortho,meta,and para positions of acetophenone were tolerated.In addition,phenylacetone,heteroaromatics and alkenes were also feasible substrates.Finally,19 arylsilanes with different substituents were synthesized,and the data were characterized by ¹H NMR,¹³C NMR.Next,we carried out the transformation and application reaction of arylsilanes,the removal of the directing group and the conversion of C-Si bond to C-I bond were successfully realized under simple conditions.Finally,the reaction mechanism of this method was studied.On the basis of previous work and control experiments,we propose a reasonable reaction mechanism:it mainly experiences the processes of C-H activation,transfermetalization,reduction and elimination.