Catalyst-Free Approach for Hydroboration of Carboxylic Acids under Mild Conditions

Abstract

Herein, we present a facile method for deoxygenative hydroboration of a broad range of carboxylic acids under very mild conditions. The most striking feature of this attractive hydroboration is that this elusive and challenging transformation was realized without catalyst and solvent. The investigation of solvent effect showed that tetrahydrofuran was also suitable for this kind of reaction. Moreover, a successful gram-scale trial may provide a very promising toolkit for carboxylic acid reduction at a large scale.

The Hidden Role of Boranes and Borohydrides in Hydroboration Catalysis

“…aldehyde, 1 h, rt) 52 and should be taken into account when devising new catalysts for these transformations (Scheme 5). [52][53][54][55][56][57] Dilution of the reaction mixture reduces the yield of hydroboration. 55 Borohydrides are active catalysts for carbonyl hydroboration (e.g.…”

“…[52][53][54][55][56][57] Dilution of the reaction mixture reduces the yield of hydroboration. 55 Borohydrides are active catalysts for carbonyl hydroboration (e.g. aldehyde, 5 min, rt); 25 Metal alkoxides can be used to promote the hydroboration of carbonyl derivatives by HBcat 18 and HBpin.…”

Reported Catalytic Hydrofunctionalizations that Proceed in the Absence of Catalysts: The Importance of Control Experiments

“…The reduction of carboxylic acids to the corresponding alkyl boronate esters using HBpin has been widely explored in organic synthesis. Alkyl boronate esters can be easily synthesized by reduction of carboxylic acid in the absence of a catalyst, and under neat conditions, as shown in Table 1, entry 1 [7] and entry 2 [8] . However, the same reaction was reported using various catalysts like Mn‐catalyst (entry 3), [9] [Ru( p ‐cymene)Cl 2 ] 2 (entry 4), [10] homogeneous Mn‐based catalysts (entry 5), [11] etc.…”

Rare‐earth metal‐catalyzed hydroboration of unsaturated compounds

“…Still, there are a lot of questions to be answered, and the hydroboration of challenging chemical bonds remains considerably unexplored compared with hydroboration of alkenes and alkynes, such as reaction mechanisms and direct hydroboration of carboxylic acids. [ 49 ] Regardless, the currently developed approaches have showcased the great capability of lanthanide complexes in promoting various organic transformations and shed a light on the fundamental principles of these transformations, accelerating the development of more transformations and applications with appreciable novelty and practicability.…”