Metal-Free Protodeboronation of Electron-Rich Arene Boronic Acids and Its Application to ortho-Functionalization of Electron-Rich Arenes Using a Boronic Acid as a Blocking Group

Abstract

The metal-free thermal protodeboronation of various electron-rich arene boronic acids was studied. Several reaction parameters controlling this protodeboronation, such as solvent, temperature, and a proton source, have been investigated. On the basis of these studies, suitable reaction conditions for protodeboronation of several types of electron-rich arene boronic acids were provided. On the basis of this protodeboronation, a new protocol for the synthesis of ortho-functionalized electron-rich arenes from these boronic acids was developed using the boronic acid moiety as a blocking group in the electrophilic aromatic substitution reaction, followed by the removal of the boronic acid moiety via thermal protodeboronation. Mechanistic studies suggested that this protodeboronation might proceed via the complex formation of a boronic acid with a proton source, followed by the carbon-boron bond fission through σ-bond metathesis, to afford the corresponding arene compound and boric acid.

meta‐Nitration of Arenes Bearing ortho/para Directing Group(s) Using C−H Borylation

“…This could due to the lack of reactivity of the boronate esters (Bpin) when compared to the free boronic acid derivatives or due to mechanistic reasons in some cases . We found an isolated single example wherein N , N ‐dimethylaniline functionalized with −Bpin at the para ‐position, when subjected to C−H nitration using AgNO 3 and NBS, predominantly produced the ipso ‐nitration product instead of the desired isomer . However, when we subjected these conditions to the crude boronate obtained from the iridium‐catalyzed reaction, the reaction failed with no traces of the desired product.…”

“…[10d] We found an isolated single example wherein N,N-dimethylaniline functionalized with ÀBpina tt he paraposition, when subjected to CÀHn itration using AgNO 3 and NBS, predominantly produced the ipsonitration product instead of the desired isomer. [14] However,w hen we subjected these conditions to the crude boronate obtained from the iridium-catalyzed reaction, the reaction failed with no traces of the desired product. Later,w es tarted at horough investigation of conditions for converting the crude boronates obtained by the CÀHb orylation of arenes to nitroarenes using coppercatalysis.…”

Harnessing C–H Borylation/Deborylation for Selective Deuteration, Synthesis of Boronate Esters, and Late Stage Functionalization

“…9 Alternatively, electron-rich boronic acids can be deborylated using water or acetic acid as the proton source. 10,11 In these chemistries, the boronic ester or acid can be used for site-specific deuteration or as a blocking group that enables regioselective bromination. These features are summarized in Scheme 1.…”

Total Synthesis of Avrainvilleol

“…Reaction of the hydrazone 3 with the diortho-substituted boronic acid 2 could lead to avrainvilleol after removal of the methyl ethers. Alternatively, hydrazone 4 and known boronic acid 5 could be merged to give rise to 1 . Preliminary and subsequent reports of these hydrazone/boronic acid couplings revealed that a single ortho-, meta-, or para-substituent was well tolerated in either the hydrazone or boronic acid coupling partner.…”