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Boron Recycling in the Metal-Free Transfer C–H Borylation of Terminal Alkynes and Heteroarenes

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posted on 14.09.2020, 17:36 authored by Vincent Desrosiers, Cecilia Zavaleta Garcia, Frédéric-Georges Fontaine
Transfer C–H borylation is an isodesmic approach to the borylation reaction using B–C-containing molecules as boron sources. In this work, we report that 2-mercaptothiazole and other analogues are active for the metal-free borylation of heterocycles and terminal alkynes. Alkynes are challenging substrates to C–H borylate because they undergo side reactions with most borylating agents. The ability of these metal-free catalysts to activate B–C bonds can also be translated to the activation of B–O bonds in the products of the 1,4-conjugate addition of alkynylboranes to chalcones. It is therefore possible to prepare β-alkynylketones from the corresponding alkynes in a process where the boron source is used in substoichiometric amounts. The mechanism and degradation patterns of these catalytic transformations have been investigated.