Efficient Construction Of α-Halogenated Boronic Esters Via Visible Light-Induced C-H Bromination

In recent years,the reactions involving organoboron compounds have attracted increasing attention in area of organic chemistry.Organoboron compounds are widely used in organic synthesis,functional materials chemistry,pharmaceutical and pesticide synthesis and biology.Among them,α-haloboronic esters are a special class of precursors,which play an important role in many reactions as ambiphilic reagents.For example,they can be used in transition metal-catalyzed C–C bond coupling and reaction with amines to obtain potentially biologically active α-aminoboronic acid derivatives.In the last few decades,chemists have devoted themselves to the synthesis of α-haloboronic esters,but these currently available methods have some limitations such as the tedious preparation of the starting materials,harsh reaction conditions,and the difficulty in further diversification of the products.Thus,the synthetic potential ofα-halogenated boronic esters is restrained by the limited preparation methods.Therefore,it is important to develop synthetic methods for α-haloboronic esters that are environmentally friendly and efficient with mild reaction conditions and ease of conversion of the products.In this thesis,we focus on the synthesis of α-halogenated boronic esters.By using benzyl boronic esters bearing different substituents as starting materials,a series of α-halogenated boronic esters were synthesized after optimizing the conditions under irradiation conditions with a halogenation reagent.This study provides a new route for the synthesis of α-bromoboronic esters,which could serve as starting materials for transition metal-catalyzed reductive coupling and 1,2-migration reactions of boronic ester compounds.This thesis is divided into three chapters:In Chapter 1,the classical transformation of organoboron compounds is briefly introduced.The applications and the current situation of the research on the synthesis of α-halogenated boron compounds are reviewed.In Chapter 2,a visible-light-induced α-bromination reaction of benzylboronic esters is developed.This reaction synthesizes a series of α-brominated boronic ester compounds under photoinduced conditions using simple and readily available boronic ester substrates in the presence of a bromination reagent.The reaction features high efficiency,mild conditions,simple operation and good substrate compatibility.In Chapter 3,based on the work in the previous chapter,the chlorination and iodination reactions of α-bromoboronic esters were further developed.The reaction underwent a halogen exchange process to give a series of α-chloro and iodosubstituted boronic ester compounds in excellent yields,thus tuning the activity of α-halogenated boronic acid esters in subsequent transformations.