Study On 1,1-diboration Of Terminal Alkynes And C─H Borylation Of Arenes

Organoborate esters are an important class of organic synthesis intermediates and are widely used in chemical,pharmaceutical and material fields.Alkenyl gemodiborates and arylborates are important synthetic building blocks for the preparation of polysubstituted alkenes and aromatics.Due to the high atom economy,the C-H boronation/hydroboration of terminal alkynes and the C-H boronation of aromatics are undoubtedly the most ideal synthesis methods for these two types of compounds.At present,although these two types of reactions have been reported,most of them require expensive transition metal catalysis.The transformation of terminal alkynes and arenes into alkenyl gemodiborates and arylborates using simple and inexpensive transition metal or metal-free catalysis is of great scientific and economic value.In this paper,the boronation of terminal alkynes and arenes is discussed in detail,and the related researches on the carbon-hydrogen bond boronation of terminal alkynes and arenes catalyzed by simple and inexpensive transition metals or non-metals are carried out.The research results obtained are as follows:1.Zinc triflate-catalyzed 1,1-bisboration of terminal alkynes.Using low-equivalent zinc trifluoromethanesulfonate as catalyst,~nOctane as solvent,1,1-diboration of terminal alkyne and pinacol borane to obtain alkenyl gemodiboronate.The reaction conditions are simple and have good functional group compatibility,which provides a simple and efficient synthesis method for alkenyl geminal diboronates.2.Metal-free carbon-hydrogen boronation of aromatic hydrocarbons.Using di-tert-butyl peroxide as the free radical initiator,the carbon-hydrogen bond boronation of toluene and pinacol biborate in air atmosphere gave good yields of ortho-,meta-and para-substituted boronations product.Other simple aromatic compounds give arylboronic esters in moderate or below moderate yields under these reaction conditions.Under the conditions of visible light-induced oxygen participation,using tetrabromofluorescein as a photocatalyst,toluene and ~oXylene can undergo a carbon-hydrogen bond boronation reaction with pinacol biborate at room temperature.