A Chemoselective Polarity-Mismatched Photocatalytic C(sp3 )-C(sp2 ) Cross-Coupling Enabled by Synergistic Boron Activation

We report the development of a C(sp3 )-C(sp2 ) coupling reaction using styrene boronic acids and redox-active esters under photoredox catalysis. The reaction proceeds through an unusual polarity-mismatched radical addition mechanism that is orthogonal to established processes. Synergistic activation of the radical precursor and organoboron are critical mechanistic events. Activation of an N-hydroxyphthalimide (NHPI) ester by coordination to boron enables electron transfer, with decomposition leading to a nucleofuge rebound, activating the organoboron to radical addition. The unique mechanism enables chemoselective coupling of styrene boronic acids in the presence of other alkene radical acceptors. The scope and limitations of the reaction, and a detailed mechanistic investigation are presented.

Boronic Ester Enabled [2 + 2]-Cycloadditions by Temporary Coordination: Synthesis of Artochamin J and Piperarborenine B

A strategy for the photosensitized cycloaddition of alkenylboronates and allylic alcohols by a temporary coordination is presented. The process allows for the synthesis of a diverse range of cyclobutylboronates. Key to development of these reactions is the temporary coordination of the allylic alcohol to the Bpin unit. This not only allows for the reaction to proceed in an intramolecular manner but also allows for high levels of stereo and regiocontrol. A key aspect of these studies is the utility of the cycloadducts in the synthesis of complex natural products artochamin J and piperarborenine B.

Unified Total Synthesis of the Limonoid Alkaloids: Strategies for the De Novo Synthesis of Highly Substituted Pyridine Scaffolds

Highly substituted pyridine scaffolds are found in many biologically active natural products and therapeutics. Accordingly, numerous complementary de novo approaches to obtain differentially substituted pyridines have been disclosed. This article delineates the evolution of the synthetic strategies designed to assemble the demanding tetrasubstituted pyridine core present in the limonoid alkaloids isolated from Xylocarpus granatum, including xylogranatopyridine B, granatumine A and related congeners. In addition, NMR calculations suggested structural misassignment of several limonoid alkaloids, and predicted their C3-epimers as the correct structures, which was further validated unequivocally through chemical synthesis. The materials produced in this study were evaluated for cytotoxicity, anti-oxidant effects, anti-inflammatory action, PTP1B and Nlrp3 inflammasome inhibition, which led to compelling anti-inflammatory activity and anti-oxidant effects being discovered.

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.

Cycloadditions of Alkenylboronic Derivatives

The literature on cycloaddition reactions of boron-containing alkenes is surveyed with 132 references. The data are categorized according to the reaction type ([2+1], [2+2], [3+2], [4+2], and [4+3] cycloadditions). The cyclopropanation and the Diels–Alder reactions of alkenylboronic derivatives have been studied more or less comprehensively, and for some substrates, they can be considered as convenient methods for the rapid regio- and stereoselective construction of even complex cyclic systems. Other types of the cycloadditions, as well as mechanistic aspects of the processes, have been addressed less thoroughly in the previous works.

1 Introduction

2 [2+1] Cycloaddition

2.1 Cyclopropanation

2.1.1 With Methylene Synthetic Equivalents

2.1.2 With Substituted Carbenoids

2.2 Epoxidation

2.3 Aziridination

3 [2+2] Cycloaddition

4 [3+2] Cycloaddition

4.1 With Nitrile Oxides

4.2 With Diazoalkanes

4.3 With Nitrones

4.4 With Azomethine Ylides

5 [4+2] Cycloaddition

6 [4+3] Cycloaddition

7 Conclusions and Outlook

Regio- and Diastereoselective Synthesis of Cyclohexadienylborons via an Intermolecular Diels-Alder Reaction of Alkenyl MIDA Boronates with 2-Pyrones

An efficient synthesis of highly functionalized cyclohexadienylborons via an inverse electron-demand Diels-Alder reaction/CO₂ extrusion of alkenyl MIDA boronates with 2-pyrones is outlined. By controlling the reaction temperature, the corresponding C(sp³ )-rich bicyclolactones could also be readily formed. The exo-selective reactions feature good functional-group tolerance, broad substrate scope, and excellent regio- and diastereoselectivity. Oxidation of the cyclohexadienylborons in a one-pot procedure led to the construction of aromatic boronates bearing valuable functional groups. Synthetic transformations of the C-B bond were demonstrated.

A stereoselective synthesis of (E)- or (Z)-β-arylvinyl halides via a borylative coupling/halodeborylation protocol

A new highly selective method for the synthesis of (E)-arylvinyl iodides and (E)- or (Z)-β-arylvinyl bromides from easily accessible styrenes and vinyl boronates, on the basis of a one-pot procedure via borylative coupling/halodeborylation is reported.

Synthesis of Aminoboronic Acid Derivatives from Amines and Amphoteric Boryl Carbonyl Compounds

Herein, we demonstrate the use of α-boryl aldehydes and acyl boronates in the synthesis of aminoboronic acid derivatives. This work highlights the untapped potential of boron-substituted iminium ions and offers insights into the behavior of N-methyliminodiacetyl (MIDA) boronates during condensation and tautomerization processes. The preparative value of this contribution lies in the demonstration that various amines, including linear and cyclic peptides, can be readily conjugated with boron-containing fragments. A mild deprotection of amino MIDA-boronates enables access to α- and β-aminoboronic acids in high chemical yields. This simple process should be applicable to the synthesis of a wide range of bioactive molecules as well as precursors for cross-coupling reactions.