Gold-Catalyzed Proto- and Deuterodeboronation

Arylboronic Acid Deborylation Deuteration via Synergistic Thiol, Lewis Base, and Photoredox Catalysis

A mild method for the deborylation deuteration of arylboronic acids with D₂O, mediated by the synergistic combination of a thiol, a Lewis base, and photoredox catalysis, is reported. This reaction showed a broad substrate scope, excellent deuterium incorporation, and functional group tolerance. Therefore, this method is practical for the site-selective D-labeling of bioactive molecules and drug molecules.

Rh-Catalyzed Coupling of Aldehydes with Allylboronates Enables Facile Access to Ketones

We present herein a novel strategy for the preparation of ketones from aldehydes and allylic boronicesters. This reaction involves the allylation of aldehydes with allylic boronicesters and the Rh-catalyzed chain-walking of homoallylic alcohols. The key to this successful development is the protodeboronation of alkenyl borylether intermediate via a tetravalent borate anion species in the presence of KHF 2 and MeOH. This approach features mild reaction conditions, broad substrate scope, and excellent functional group tolerance. Mechanistic studies also supported that the tandem allylation and chain-walking process was involved.

Transmetalation of boronic acids and their derivatives: mechanistic elucidation and relevance to catalysis

The Suzuki-Miyaura reaction (the cross-coupling reaction of boronic acids with organic halides catalysed by Pd complexes) has been recognised as a useful synthetic organic reaction that forms a C(sp²)-C(sp²) bond. The catalytic cycle of the reaction involves the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. It migrates the aryl and alkenyl groups of boronic acid to Pd and produces a Pd-C bond. Many studies have investigated the mechanism of transmetalation. They elucidated the mechanism of the organometallic reaction and its role as a fundamental step in catalytic reactions. This perspective reviews studies on the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. Emphasis was laid on the structures and chemical properties of the intermediate Pd complexes and the effects of OH^- on the pathways of the catalytic Suzuki-Miyaura reaction. The reactions of arylboronic acids with Rh(I)-OH complexes were investigated, which are relevant to the mechanism of Rh-catalysed addition of aryl boronic acids to enones and aldehydes. Recent studies on the transmetalation of boronic acids with other late transition metals such as Fe(II), Co(I), Pt(II), Au(III), and Au(I) are presented with the related catalytic reactions and their utilisation in the synthesis of aromatic molecules and π-conjugated materials.

Light-driven decarboxylative deuteration enabled by a divergently engineered photodecarboxylase

Despite the well-established chemical processes for C-D bond formation, the toolbox of enzymatic methodologies for deuterium incorporation has remained underdeveloped. Here we describe a photodecarboxylase from Chlorella variabilis NC64A (CvFAP)-catalyzed approach for the decarboxylative deuteration of various carboxylic acids by employing D2O as a cheap and readily available deuterium source. Divergent protein engineering of WT-CvFAP is implemented using Focused Rational Iterative Site-specific Mutagenesis (FRISM) as a strategy for expanding the substrate scope. Using specific mutants, several series of substrates including different chain length acids, racemic substrates as well as bulky cyclic acids are successfully converted into the deuterated products (>40 examples). In many cases WT-CvFAP fails completely. This approach also enables the enantiocomplementary kinetic resolution of racemic acids to afford chiral deuterated products, which can hardly be accomplished by existing methods. MD simulations explain the results of improved catalytic activity and stereoselectivity of WT CvFAP and mutants.

Cobalt-Catalyzed Protodeboronation of Aryl and Vinyl Boronates

An efficient cobalt-based catalytic system for protodeboronation of various aryl and vinyl boronates is described. The reaction is capable of tolerating a wide range of functional groups. The reaction is also extended to deuterodeboronation with D₂O, which provides a potential protocol for the synthesis of regiospecifically deuterated arenes and olefins.

Catalyst-free reductive hydrogenation or deuteration of aryl–heteroatom bonds induced by light

The photoinduced hydrogenation or deuteration of quaternary arylammonium salts, aryl triflates, and aryl halides under catalyst-free conditions was achieved.

Trimethyl 4,4′,4′′-(ethene-1,1,2-triyl)tribenzoate

The tandem in situ double Suzuki coupling reaction of a diborated ethyl­ene compound containing electron-withdrawing aromatic ester groups was studied. The major product is derived from the Suzuki coupling involving the boryl group and an aryl­iodide derivative followed by preferential protodeboronation of the second boryl ligand.

The title compound, C₂₆H₂₂O₆, is formed as the major product from the reaction between syn-1,2-bis­(pinacolatoboron)-1,2-bis­(4-methyl­carb­oxy­phen­yl)ethene and excess methyl 4-iodo­benzoate in basic DMSO using a palladium catalyst at 80°C via Suzuki coupling followed by protodeboronation. Crystals were grown by slow evaporation of a hexa­nes solution at room temperature.

Indolylboronic Acids: Preparation and Applications

Indole derivatives are associated with a variety of both biological activities and applications in the field of material chemistry. A number of different strategies for synthesizing substituted indoles by means of the reactions of indolylboronic acids with electrophilic compounds are considered the methods of choice for modifying indoles because indolylboronic acids are easily available, stable, non-toxic and new reactions using indolylboronic acids have been described in the literature. Thus, the aim of this review is to summarize the methods available for the preparation of indolylboronic acids as well as their chemical transformations. The review covers the period 2010-2019.

Dual copper- and photoredox-catalysed C(sp2)–C(sp3) coupling

The use of copper catalysis with visible light photoredox catalysis in a cooperative fashion has recently emerged as a versatile means of developing new C–C bond forming reactions. In this work, dual copper and photoredox catalysis is exploited to effect C(sp²)–C(sp³) cross-couplings between aryl boronic acids and benzyl bromides.

Rapid Iododeboronation with and without Gold Catalysis: Application to Radiolabelling of Arenes

Radiopharmaceuticals that incorporate radioactive iodine in combination with single‐photon emission computed tomography imaging play a key role in nuclear medicine, with applications in drug development and disease diagnosis. Despite this importance, there are relatively few general methods for the incorporation of radioiodine into small molecules. This work reports a rapid air‐ and moisture‐stable ipso‐iododeboronation procedure that uses NIS in the non‐toxic, green solvent dimethyl carbonate. The fast reaction and mild conditions of the gold‐catalysed method led to the development of a highly efficient process for the radiolabelling of arenes, which constitutes the first example of an application of homogenous gold catalysis to selective radiosynthesis. This was exemplified by the efficient synthesis of radiolabelled meta‐[¹²⁵I]iodobenzylguanidine, a radiopharmaceutical that is used for the imaging and therapy of human norepinephrine transporter‐expressing tumours.

Auto-Tandem Catalysis: PdII -Catalysed Dehydrogenation/Oxidative Heck Reaction of Cyclopentane-1,3-diones

A Pd^II catalyst system has been used to successfully catalyse two mechanistically distinct reactions in a one-pot procedure: dehydrogenation of 2,2-disubstituted cyclopentane-1,3-diones and the subsequent oxidative Heck coupling. This auto-tandem catalytic reaction is applicable to both batch and continuous flow processes, with the latter being the first example of a tandem aerobic dehydrogenation/oxidative Heck in flow. In addition, a telescoped reaction involving enantioselective desymmetrisation of the all-C quaternary centre was successfully achieved.

Base-Catalyzed Aryl-B(OH)2 Protodeboronation Revisited: From Concerted Proton Transfer to Liberation of a Transient Aryl Anion

Pioneering studies by Kuivila, published more than 50 years ago, suggested ipso protonation of the boronate as the mechanism for base-catalyzed protodeboronation of arylboronic acids. However, the study was limited to UV spectrophotometric analysis under acidic conditions, and the aqueous association constants (K_a) were estimated. By means of NMR, stopped-flow IR, and quenched-flow techniques, the kinetics of base-catalyzed protodeboronation of 30 different arylboronic acids has now been determined at pH > 13 in aqueous dioxane at 70 °C. Included in the study are all 20 isomers of C₆H_nF_(5-n)B(OH)₂ with half-lives spanning 9 orders of magnitude: <3 ms to 6.5 months. In combination with pH-rate profiles, pK_a and ΔS^⧧ values, kinetic isotope effects (²H, ¹⁰B, ¹³C), linear free-energy relationships, and density functional theory calculations, we have identified a mechanistic regime involving unimolecular heterolysis of the boronate competing with concerted ipso protonation/C-B cleavage. The relative Lewis acidities of arylboronic acids do not correlate with their protodeboronation rates, especially when ortho substituents are present. Notably, 3,5-dinitrophenylboronic acid is orders of magnitude more stable than tetra- and pentafluorophenylboronic acids but has a similar pK_a.

Dual gold photoredox C(sp2)–C(sp2) cross couplings – development and mechanistic studies

A new oxidant- and base-free dual catalysed C(sp²)–C(sp²) coupling between arylboronic acids and aryldiazonium salts has been developed. Mechanistic investigations reveal two divergent pathways depending on the gold catalyst employed.

Regio- and stereoselective synthesis of conjugated trienes from silaborated 1,3-enynes

Palladium-catalyzed silaboration of 1,3-enynes followed by Suzuki–Miyaura coupling with alkenyl iodides and Hiyama coupling with aryl iodides provides access to 1,3,5-trienes with defined regio- and stereochemistry.

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

Ir-catalyzed deborylation can be used to selectively deuterate aromatic and heteroaromatic substrates. Combined with the selectivities of Ir-catalyzed C-H borylations, uniquely labeled compounds can be prepared. In addition, diborylation/deborylation reactions provide monoborylated regioisomers that complement those prepared by C-H borylation. Comparisons between Ir-catalyzed deborylations and Pd-catalyzed deborylations of diborylated indoles described by Movassaghi are made. The Ir-catalyzed process is more effective for deborylating aromatics and is generally more effective in the monodeborylation of diborylated thiophenes. These processes can be applied to complex molecules such as clopidogrel.