An Organoborane Vinyl Monomer with Styrene-like Radical Reactivity: Reactivity Ratios and Role of Aromaticity

Ring-Opening Metathesis Polymerization of the Dewar Isomer of 1,2-Azaborinine, a B-N Isostere of Benzene

The successful polymerization of the Dewar isomer of an azaborinine heterocycle is reported. Controlled ring-opening metathesis polymerization was accomplished with Grubbs and Hoveya-Grubbs second generation catalysts (G2, HG2), as well as a Z-selective Ru catalyst (HGM2001). The structure of the polymers containing 4-membered B-N heterocycles was verified by GPC and multinuclear and 2D NMR. Differences in stereochemistry of polymers derived from G2/HG2 versus the Z-selective catalyst HGM2001 were substantiated by 2D NOESY, FT-IR, and Raman analyses. The incorporation of B-N heterocycles into these polymer structures is promising as a route to functional polymers that contain polar side groups.

Azaborine Isomer Effects on Benzylic Ion Stability and Reactivity: Consequences for BN2VN Ionic Polymerization

Benzylic cations and anions are implicated in the mechanism of critical organic transformations, such as styrene polymerization. We investigate the influence of BN for CC bond substitution on the reactivity...

Photoinduced SET to access olefin-acrylate copolymers

Single-electron transfer (SET)-induced decarboxylative backbone radical generation was exploited to produce statistical olefin-acrylate copolymers. Quenching of the backbone radical with an H atom donor yielded ethylene or propylene repeat units.

Enantioselective Synthesis of Oxazaborolidines by Palladium-Catalyzed N-H/B-H Double Activation of 1,2-Azaborines

A palladium-catalyzed N-H/B-H double activation of 1,2-dihydro-1,2-benzazaborines proceeded via cycloaddition with vinyl ethylene carbonate to produce polycyclic oxazaborolidines in 31-96 % yield. The key step in this process is the release of molecular hydrogen from a borate intermediate. Using a SPINOL-derived phosphoramidite as a chiral ligand, chiral oxazaborolidines were synthesized in good to high yields with excellent enantioselectivity (up to 95 % ee). The vinyl group of the resulting oxazaborolidine underwent metathesis, Heck reaction, and Wacker oxidation without affecting the oxazaborolidine framework.

Vinylboronic acid pinacol ester as a vinyl alcohol-precursor monomer in radical copolymerization with styrene

The use of vinylboronic acid pinacol ester (VBpin) as a comonomer and post-polymerization oxidation afforded vinyl alcohol (VA)-styrene copolymers, which were difficult to synthesize using a typical VA precursor monomer, vinyl acetate (VAc). The molar mass was controllable by applying RAFT polymerization and the VA composition ratio could be tuned from 11% to 72%. The solubility and glass-transition temperature were also evaluated with the copolymers of different composition ratios.

Mono- and Dinitro-BN-Naphthalenes: Formation and Characterization

Mono- and dinitro-BN-naphthalenes, i.e., 1-nitro-, 3-nitro-, 1,6-dinitro-, 3,6-dinitro-, and 1,8-dinitro-BNN, were generated in the nitration of 9,10-BN-naphthalene (BNN), a boron–nitrogen (BN) bond-embedded naphthalene, with AcONO₂ and NO₂BF₄ in acetonitrile. The nitrated products were isolated and characterized by NMR, GC-MS, IR, and X-ray single crystallography. The effects of the nitration on the electron density and aromaticity of BNN were evaluated by B-11 NMR analysis and HOMA calculations.

Elucidating Monomer Character of an Alkenyl Boronate through Radical Copolymerization Leads to Copolymer Synthesis beyond the Limitation of Copolymerizability by Side-Chain Replacement

Isopropenyl boronic acid pinacol ester (IPBpin) was used as a comonomer in radical polymerization with a wide range of common vinyl monomers for elucidation of the monomer character and syntheses of conventionally inaccessible copolymers via the replacement of the boron pendant. The study revealed that the boron-containing monomer is categorized into an electron-rich conjugated monomer, which was well consistent with the results of density functional theory (DFT)-based investigation. One of the thus obtained copolymers, the IPBpin-styrene copolymer, was successfully transformed into an α-methyl vinyl alcohol (MVA)-styrene counterpart via oxidation of the boron pendant. The copolymer cannot be synthesized even with the acetyl-protected monomer instead of IPBpin due to poor copolymerization ability based on the nonconjugated character.

1,2-Azaborine's Distinct Electronic Structure Unlocks Two New Regioisomeric Building Blocks via Resolution Chemistry

Two new 1,2-azaborine building blocks that enable the broad diversification of previously not readily accessible C4 and C5 ring positions of the 1,2-azaborine heterocycle are developed. 1,2-Azaborine's distinct electronic structure allowed the resolution of a mixture of C4- and C5-borylated 1,2-azaborines. The connection between the electronic structure of C4 and C5 positions of 1,2-azaborine and their distinct reactivity patterns is revealed by a combination of reactivity studies and kinetic measurements that are supported by DFT calculations. Specifically, we show that oxidation by N-methylmorpholine N-oxide (NMO) is selective for the C4-borylated 1,2-azaborine, and the Ir-catalyzed deborylation is selective for the C5-borylated 1,2-azaborine via kinetically controlled processes. On the other hand, ligand exchange with diethanolamine takes place selectively with the C4-borylated isomer via a thermodynamically controlled process. These results represent the first examples for chemically distinguishing a mixture of two aryl mono-Bpin-substituted isomers.

BN Polystyrenes: Emerging Optical Materials and Versatile Intermediates

BN polystyrenes are an emerging class of polyolefins functionalized with aromatic side chains in which at least one CC bond is replaced with a BN bond. This class of structures exhibits unusual photophysical properties relative to organic polymers. BN polystyrenes serve as intermediates in the preparation of functional polymers, including stereoregular polar polyolefins. The consequences of BN for CC bond substitution on reactivity and properties are highlighted.

Late-stage functionalization of BN-heterocycles

BN/CC isosterism has emerged as a viable strategy to expand the chemical space of organic molecules. In particular, the application of BN/CC isosterism to arenes has received significant attention due to the vast available chemical space provided by aromatic hydrocarbons. The synthetic efforts directed at assembling novel aromatic BN heterocycles have resulted in the discovery of new properties and functions in a variety of fields including biomedical research, medicinal chemistry, materials science, catalysis, and organic synthesis. This tutorial review specifically covers recent advances in synthetic technologies that functionalize assembled boron-nitrogen (BN) heterocycles and highlights their distinct reactivity and selectivity in comparison to their carbonaceous counterparts. It is intended to serve as a state-of-the-art compendium for readers who are interested in the reaction chemistry of BN heterocycles.