Reductive stereo- and regiocontrolled boryllithiation and borylsodiation of arylacetylenes using flow microreactors

Abstract

Given their prevalence within valuable organic compounds, constructing multisubstituted alkenes while stereo- and regiochemically controlling the substituents on the alkene stands as a pivotal objective in organic synthesis. Now, the stereo- and regioselective syn-boryllithiation and syn-borylsodiation of arylacetylenes have been achieved by reductive borylmetallation using flow microreactors. This method involves the fast mixing of a solution of an alkyne and stoichiometric alkoxypinacolborane with an alkali metal arenide solution, which efficiently generates highly reactive β-borylalkenyllithium and β-borylalkenylsodium species by suppressing the undesired diboration that inevitably occurs in a batch reactor. Unlike conventional three-component borofunctionalization, the intermediates can be generated in the absence of electrophiles, which has enabled diverse electrophiles to participate in various syn-borofunctionalizations such as borylsilylation, borylhalogenation, borylcarbonylation, borylsulfenylation and borylarylation. Trapping with aldehydes and ketones provides a series of oxaboroles of biological interest. Furthermore, unsymmetric diarylacetylenes undergo highly regioselective borylmetallation, which is applicable to the stereo- and regiocontrolled syntheses of multisubstituted oxaboroles and differently tetrasubstituted alkenes.