Direct nucleophilic and electrophilic activation of alcohols using a unified boron-based organocatalyst scaffold

LuCl3/B(C6F5)3 Cocatalyzed Reductive Deoxygenation of Ketones, Aldehydes, Alcohols, and Ethers to Alkanes with Pinacolborane

This report describes the LuCl3/B(C6F5)3 cocatalyzed reductive deoxygenation of 67 ketones, aldehydes, alcohols, and ethers to alkanes under mild conditions. The strategy tolerates reactive amino, hydroxyl, nitro, halogen, vinyl, and ester functional groups, and the results demonstrate rare chemoselective deoxygenation of α,β-unsaturated ketones. Isotopic labeling experiments, control experiments, and derivatization studies are used to elucidate the reaction mechanism.

Cooperative Diarylborinic Acid/Chloride-Catalyzed Formal SNi Reaction of cis-4-Hydroxymethyl-1,2-Cyclopentene Oxides

A catalytic formal SNi reaction was designed to achieve stereoretentive products for cis-4-hydroxymethyl-1,2-cyclopentene oxides by using diarylborinic acid as a dual role catalyst and chloride as a catalytic transient nucleophile through a double-displacement mechanism. This reaction offers the advantages of a low catalyst loading of 0.1 mol % and wide substrate scope, even including N-substituents. The use of chiral boron acid as a catalyst for this reaction was also attempted.

Removing Neighboring Ring Influence in Monocyclic B-OH Diazaborines: Properties and Reactivity as Phenolic Bioisosteres with Dynamic Hydroxy Exchange

The design of small molecules with unique geometric profiles or molecular connectivity represents an intriguing yet neglected challenge in modern organic synthesis. This challenge is compounded when emphasis is placed on the preparation of new chemotypes that have distinct and practical functions. To expand the structural diversity of boron-containing heterocycles, we report herein the preparation of novel monocyclic hemiboronic acids, diazaborines. These compounds have enabled the study of a pseudoaromatic boranol-containing (B-OH) ring free of influence from an appended aromatic system. Synthetic and spectroscopic studies have provided insight into the aromatic character, Lewis acidic nature, chemical reactivity, and unique ability of the exocyclic B-OH unit to participate in hydroxy exchange, suggesting their use in organocatalysis and as reversible covalent inhibitors. Moreover, density functional theory and nucleus-independent chemical shift calculations reveal that the aromatic character of the boroheterocyclic ring is increased significantly in comparison to known bicyclic benzodiazaborines (naphthoid congeners), consequently leading to attenuated Lewis acidity. Direct structural comparison to a well-established biaryl isostere, 2-phenylphenol, through X-ray crystallographic analysis reveals that N-aryl derivatives are strikingly similar in size and conformation, with attenuated logP values underscoring the value of the polar BNN unit. Their potential application as low-molecular-weight scaffolds in drug discovery is demonstrated through orthogonal diversification and preliminary antifungal evaluation (Candida albicans), which unveiled analogs with low micromolar inhibitory concentration.

Modular Synthesis of Complex Benzoxaboraheterocycles through Chelation-Assisted Rh-Catalyzed [2 + 2 + 2] Cycloaddition

Benzoxaboraheterocycles (BOBs) are moieties of increasing interest in the pharmaceutical industry; however, the synthesis of these compounds is often difficult or impractical due to the sensitivity of the boron moiety, the requirement for metalation-borylation protocols, and lengthy syntheses. We report a straightforward, modular approach that enables access to complex examples of the BOB framework through a Rh-catalyzed [2 + 2 + 2] cycloaddition using MIDA-protected alkyne boronic acids. The key to the development of this methodology was overcoming the steric barrier to catalysis by leveraging chelation assistance. We show the utility of the method through synthesis of a broad range of BOB scaffolds, mechanistic information on the chelation effect, intramolecular alcohol-assisted BMIDA hydrolysis, and linear/cyclic BOB limits as well as comparative binding affinities of the product BOB frameworks for ribose-derived biomolecules.

Diarylborinic Acid-Catalyzed Ring Opening of cis-4-Hydroxymethyl-1,2-Cyclopentene Oxides: Synthesis of 1,2,4-Trisubstituted Cyclopentanes

A diarylborinic acid-catalyzed ring opening of cis-4-hydroxymethyl-1,2-cyclopentene oxides was developed with N-nucleophiles including anilines, benzotriazole, and alkylamines, as well as S-nucleophiles, affording 1,2,4-trisubstituted cyclopentane compounds containing a quaternary carbon center. The mechanism study indicated that the "half-cage" structure formed by the epoxide substrate and the catalyst prevents the nucleophiles from attacking the inner side of the "half-cage", resulting in the desired ring-opening product.