Boron Catalysis in the Transformation of Carboxylic Acids and Carboxylic Acid Derivatives

Abstract

Carboxylic acids, amides, and esters are ubiquitous motifs in functional organic molecules. However, the reactivities of these high oxidation state carbonyl compounds are far lower than ketones and aldehydes, and catalysts applicable to transform this class of carbonyl compounds are limited. On the other hand, boron catalysts have found various applications in the transformation of carbonyl compounds by taking advantage of the unique properties derived from their vacant p-orbitals. The continuous advancement of boron catalysis has realized several unprecedented direct transformations of carboxylic acids, amides, and esters in the past decade. In this review, representative achievements of boron catalysis are summarized according to reaction types by focusing on their applications to non-activated carboxylic acids, amides, and esters.

Less Is More: N(BOH)2 Configuration Exhibits Higher Reactivity than the B3NO2 Heterocycle in Catalytic Dehydrative Amide Formation

“…Therefore, the community has devised several catalytic systems to promote the direct amidation . Since the pioneering work reported by Yamamoto in 1996, boronic acid derivatives have captured attention because of their facile nature to fine-tune the catalyst structure. , Recent in-depth investigations led by Whiting have revealed that the active species in the boronic acid-catalyzed direct amidation is an oligomeric, highly ordered complex rather than originally proposed acyloxyboron species (Scheme a) . Later, Ishihara also reached the same conclusion .…”

Boron‐Catalyzed α‐Functionalizations of Carboxylic Acids

“…[3] The electrophilicity of carboxylic acids is enhanced by the reversible formation of boron carboxylates, thereby the Diels-Alder reaction is facilitated. Since then, boron-catalyzed electrophilic activation of carboxylic acids has found various applications, [4] including [3 + 2] dipolar cycloadditions, [3c] 1,4-addition reactions, [5] and dehydrative amidations/esterifications. [6] In contrast, the boron-catalyzed enolate formation of carboxylic acids had been almost neglected.…”

Expeditious Access to the B3NO2 Heterocycle Enabling Modular Derivatization

“…Thus, devising a catalytic variant for amidation reactions in which carboxylic acids and amines are directly condensed by a catalyst instead of a stoichiometric amount of activator is highly desirable . Since the pioneering report by Yamamoto et al revealing the specific utility of boronic acids for catalytically coupling carboxylic acids and amines without coproducing waste, a number of boronic acid derivatives and related boron-containing compounds have been reported. , The previous 5 years have witnessed the emergence of diboron compounds as superior catalysts to drive this transformation, an idea sparked by the detailed mechanistic study by Whiting and Ishihara delineating the involvement of oligomeric boron species in boronic acid catalysis (Figure ). − In 2017, our group disclosed a new molecular entity featuring a unique six-membered B 3 NO 2 heterocycle, DATB (1,3-dioxa-5-aza-2,4,6-triborinane), that exerts high catalytic efficiency in dehydrative amide bond-forming reactions with broad substrate generality …”