A Study Of Organic Radical Borylation And Several Clean And Efficient Reactions

Organic synthesis showed tremendous importance in human‘s life.On the other hand,organoboronic acids and esters are highly valuable building blocks in transition-metal-catalyzed cross-coupling reactions and various of functional group transformations.Additionally,it‘s frequently found in a series of organic drug molculars.The traditional pathway for synthesis of organoboronic compounds include electrophilic borylation of Grignard reagents or organolithium reagents,transition-metal-catalyzed C-H borylation and hydroboration of olefins.However,these methods suffer from significant limitations such as low functional group compatibility and low regioselectivity.Therefore,development of new synthesis methods for organoboronic compounds still shows significant importance.In recent years,borylation via radical intermediates has been developed as new avenues for C-B bond formation.In this article,a series of radical borylation reactions were studied.Firstly,we studied the electrochemical radical borylation of aryl iodides.Comparing with the former study,we accelerated the reaction speed from 48 h to 3 h by a constant current.Secondly,we studied the transition-metal-free borylation of alkyl halides via a radical mechanism.By using the most cheap and abundant pinacol diboron as reagent,we achieved the borylation of alkyl iodides and bromides under basic conditions through a simple and practicle procedure.It works without transition-metal,under mild conditions and tolerates a wide range of functional groups.Importantly,it‘s not sensitive to air or moisture,and easy to be enlarged.Finally,we studied the radical C-C bond cleavage ring-opening borylation reaction of cyclic hemiacetle derivates.Driven by blue visible light,we achieved the radical borylation via C-C bond cleavage ring-opening.For the above reactions,we studied the mechanism in detail by a series of methods,including the dynamic control experiments,the electron paramagnetic resonance（EPR）experiments and the density functional theory（DFT）calculations.Accordingly the mechanism was proposed,which indicated that the radical reacts with a free diboron reagent to generate the borylation product.Except for borylation reactions,this article also includes some other clean and efficient organic reactions.Firstly,we studied a general electrochemical strategy for the Sandmayer reaction.The aryl radical was formed by reducing the diazonium salt in the cathode and further caught by halogenation reagents.Comparing with the traditional Sandmayer reactions,our study works under mild conditions without transition-metal,and variety of functional groups were tolerated.Additionally,we designed the rarely used in situ EPR measurements to study the mechanism.Furthermore,we studies the direct carboxylation of the diazo group ipso-C（sp²）-H bond with CO₂.This method works without transition-metal and under mild conditions.In this study,we achieved the carboxylation-esterification,the carboxylation-amidation of diazo compounds and the bi-carboxylation-esterification of TMSCHN₂.