Synthesis of aminoboronic acids and their applications in bifunctional catalysis

Boronic acid-DMAPO cooperative catalysis for dehydrative condensation between carboxylic acids and amines

Arylboronic acid and DMAPO cooperatively catalyse the dehydrative condensation reaction between carboxylic acids and amines to give the corresponding amides under azeotropic reflux conditions. This cooperative use is much more effective than their individual use as catalysts.

Arylboronic acid and 4-(N,N-dimethylamino)pyridine N-oxide (DMAPO) cooperatively catalyse the dehydrative condensation reaction between carboxylic acids and amines to give the corresponding amides under azeotropic reflux conditions. This cooperative use is much more effective than their individual use as catalysts, and chemoselectively promotes the amide condensation of (poly)conjugated carboxylic acids. The present method is practical and scalable, and has been applied to the synthesis of sitagliptin and a drug candidate.

Boryl (Hetero)aryne Precursors as Versatile Arylation Reagents: Synthesis through C-H Activation and Orthogonal Reactivity

(Pinacolato)boryl ortho-silyl(hetero)aryl triflates are presented as a new class of building blocks for arylation. They demonstrate unique versatility by delivering boronate or (hetero)aryne reactivity chemoselectively in a broad range of transformations. This approach enables the unprecedented postfunctionalization of fluoride-activated (hetero)aryne precursors, for example, as substrates in transition-metal catalysis, and offers valuable new possibilities for aryl boronate postfunctionalization without the use of specialized protecting groups.

Hydrolysis of 8-(pinacolboranyl)quinoline: where is the 8-quinolylboronic acid?

The compound 8-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-quinoline was prepared and found to hydrolyze rapidly in air; however, the expected product (quinolin-8-yl)boronic acid was not observed. Instead, the (quinolinium-8-yl)trihydroxyborate zwitterion or an anhydride were observed depending on the conditions of hydrolysis. The two products are related to one another in the degree of hydration, and the two forms could be interconverted. Both hydrolysis products were structurally characterized. Additionally, a commercial sample of ‘8-quinolylboronic acid’ was actually found to be the anhydride. The results call into question whether monomeric (quinolin-8-yl)boronic acid can actually be isolated in the neutral Lewis base-free form.

Simple and effective label-free capillary electrophoretic analysis of sugars by complexation using quinoline boronic acids

An effective separation and detection procedure for sugars by capillary electrophoresis (CE) using a complexation between quinolineboronic acid (QBA) and multiple hydroxyl structure of sugar alcohol is reported. We investigated the variation of fluorescence spectra of a variety of QBAs with sorbitol at a wide range of pH conditions and then found that 5-isoQBA strongly enhanced the fluorescence intensity by the complexation at basic pH conditions. The other sugar alcohols having multiple hydroxyls also revealed the enhancement of the fluorescence intensity with 5-isoQBA, whereas the alternation of the intensity was not found in the sugars such as glucose. After optimization of the 5-isoQBA concentration and pH of the buffered solution in CE analysis, 6 sugar alcohols were successfully separated in the order based on the formation constants with 5-isoQBA, which were calculated from the variation of the fluorescence intensity with each sugar alcohol and 5-isoQBA. Furthermore, the limits of detection for sorbitol and xylitol by the CE method were estimated at 15 and 27 μM, respectively.

Mild arylboronic acid catalyzed selective [4 + 3] cycloadditions: access to cyclohepta[b]benzofurans and cyclohepta[b]indoles

The first example of arylboronic acid catalyzed [4 + 3] cycloaddition reaction is reported.

Direct Amide Formation from N-Arylglycine Ethyl Esters and Carboxylic Acids Catalysed by Phenylboronic Acid

The phenylboronic acid-catalysed reaction of an N-arylglycine ethyl ester with various carboxylic acids, including N-acyl- N-phenylglycines, directly affords an amide or a dipeptide in 13–73% yields.

Primary alkylboronic acids as highly active catalysts for the dehydrative amide condensation of α-hydroxycarboxylic acids

Primary alkylboronic acids such as methylboronic acid and butylboronic acid are highly active catalysts for the dehydrative amide condensation of α-hydroxycarboxylic acids. The catalytic activities of these primary alkylboronic acids are much higher than those of the previously reported arylboronic acids. The present method was easily applied to a large-scale synthesis, and 14 g of an amide was obtained in a single reaction.

Transamidation of primary amides with amines catalyzed by zirconocene dichloride

Zirconocene dichloride (Cp(2)ZrCl(2)) has been shown to be an effective catalyst for the transamidation of primary amides with amines in cyclohexane at 80 °C in 5-24 hours. For favourable substrates, the reaction can be performed at temperatures as low as 30 °C.

Complexity-generating hydration reactions via gold-catalyzed addition of boronic acids to alkynes

Boronic acids can serve as organic soluble substitutes for water molecules in the metal-catalyzed hydration of alkynes. The Au-catalyzed addition of boronic acids to alkynes provides an alternative method for enolate generation, which proceeds under exceptionally mild conditions. The resulting enolates can be trapped by aldehydes present in the reaction mixture, giving aldol products that can be isolated as cyclic borate esters. These compounds are versatile synthetic intermediates that can be elaborated into a variety of products by transformation of the boron moiety. The Au-catalyzed reaction of boronic acids with propargylic alcohols results in efficient Meyer–Schuster rearrangement to the corresponding enones. The rearrangement of tertiary alcohols gives (E)-enones with moderate to good selectivity, and the addition of a boronic acid to the reaction appears to enhance the level of geometrical control. The rearrangement of primary alcohols to terminal enones also occurs readily in the presence of catalytic Au(I) and a boronic acid, and the resulting terminal enones can be reacted with nucleophiles in one-pot procedures to give a variety of β-substituted ketones.

Boroalkyl group migration provides a versatile entry into α-aminoboronic acid derivatives

A reaction exemplifying migration of boron-substituted carbon is described. We show that α-boroalkyl groups of transient boroalkyl acyl azide intermediates readily migrate from carbon to nitrogen. This process allows access to a new class of stable molecules, α-boryl isocyanates, from α-borylcarboxylic acid precursors. The methodology facilitates synthesis of a wide range of α-aminoboronic acid derivatives, including α,α-disubstituted analogues.

Scaffolding Catalysis: Expanding the Repertoire of Bifunctional Catalysts

Inducing an intramolecular reaction is a powerful means of accelerating reactions. Though this mechanism of catalysis is common in enzymes, it is underutilized in synthetic catalysts. This article outlines our group's recent efforts to use reversible covalent bonding to induce an intramolecular reaction, allowing for rate acceleration as well as control of the selectivity in the desymmetrization of 1,2-diols.

Iridium-Catalyzed Allylic Amination Route to α-Aminoboronates: Illustration of the Decisive Role of Boron Substituents

The development of a new route to α-aminoboronates using an iridium-catalyzed allylic amination on boronated substrates is described. Unlike the boronate group, the trifluoroborato substituent was found to govern the regioselectivity exclusively in favor of branched products. The transformation of an allylic substitution product into an α-aminoboronic ester in an efficient way validated the implementation of this approach.

Synthesis of 8-arylquinolines via one-pot Pd-catalyzed borylation of quinoline-8-yl halides and subsequent Suzuki-Miyaura coupling

A one-pot process has been developed for the synthesis of 8-arylquinolines via Pd-catalyzed borylation of quinoline-8-yl halides and subsequent Suzuki-Miyaura coupling with aryl halides using n-BuPAd(2) as ligand. Yields of up to 98% were obtained.

Donor-acceptor assisted alkyne hydration: a luminescent boron-stabilized enol

An alkyne molecule 2-(2'-BMes(2)-phenylethynyl)pyridine (1) that contains a Lewis acidic BMes(2) group and a Lewis basic pyridyl group has been found to undergo facile hydration under ambient conditions in the presence of CuI, forming a highly emissive and stable enol ester (2). The lack of any hydration reactivity by a control compound 2-(2'-BMes(2)-phenylethynyl)benzene (3) under the same conditions supports that the cooperativity between the Lewis donor and acceptor groups plays a key role in the formation of 2.