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1. Opportunities Using Boron to Direct Reactivity in the Organic Solid State

   https://doi.org/10.1055/s-0040-1707297  

   Campillo-Alvarado, Gonzalo; MacGillivray, Leonard R. (April 2021, Synlett)

   null (Ed.)

   Abstract This Account describes work by our research group that highlights opportunities to utilize organoboron molecules to direct chemical reactivity in the organic solid state. Specifically, we convey a previously unexplored use of hydrogen bonding of boronic acids and boron coordination in boronic esters to achieve [2+2]-photocycloadditions in crystalline solids. Organoboron molecules act as templates or ‘shepherds’ to organize alkenes in a suitable geometry to undergo regio- and stereoselective [2+2]-photocycloadditions in quantitative yields. We also provide a selection of publications that served as an inspiration for our strategies and offer challenges and opportunities for future developments of boron in the field of materials and solid-state chemistry. 1 Introduction 1.1 Template Strategy for [2+2]-Photocycloadditions in the Solid State 2 Boronic Acids as Templates for [2+2]-Photocycloadditions in the Solid State 2.1 Supramolecular Catalysis of [2+2]-Photocycloadditions in the Solid State Using Boronic Acids 3 Boronic Esters as Templates for [2+2]-Photocycloadditions in the Solid State 3.1 Application of Photoproducts: Separation of Thiophene from Benzene through Crystallization 3.2 Crystal Reactivity of B←N-Bonded Adducts: The Case of Styryl­thiophenes 4 Conclusions and Perspectives 

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2. Dearomative C2-borylation of indoles

   https://doi.org/10.1039/D5DT00579E  

   Begum, Ayesha; Akram, Manjur O; Martin, Caleb D (April 2025, Dalton Transactions)

   The dearomative functionalization of indoles to C2-borylated indolenium compounds is achieved under mild conditions by leveraging the high Lewis acidity of bis(1-methyl-ortho-carobranyl)borane. 

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3. MIDA‐ and TIDA‐Boronates Stabilize α‐Radicals Through B−N Hyperconjugation

   https://doi.org/10.1002/anie.202309566  

   LaPorte, Antonio J.; Feldner, Jack E.; Spies, Jan C.; Maher, Tom J.; Burke, Martin D. (August 2023, Angewandte Chemie International Edition)

   Abstract Multifunctional organoboron compounds increasingly enable the simple generation of complex, Csp³‐rich small molecules. The ability of boron‐containing functional groups to modify the reactivity of α‐radicals has also enabled a myriad of chemical reactions. Boronic esters with vacant p‐orbitals have a significant stabilizing effect on α‐radicals due to delocalization of spin density into the empty orbital. The effect of coordinatively saturated derivatives, such as N‐methyliminodiacetic acid (MIDA) boronates and counterparts, remains less clear. Herein, we demonstrate that coordinatively saturated MIDA and TIDA boronates stabilize secondary alkyl α‐radicals via σ_B‐Nhyperconjugation in a manner that allows site‐selective C−H bromination. DFT calculated radical stabilization energies and spin density maps as well as LED NMR kinetic analysis of photochemical bromination rates of different boronic esters further these findings. This work clarifies that the α‐radical stabilizing effect of boronic esters does not only proceed via delocalization of radical character into vacant boron p‐orbitals, but that hyperconjugation of tetrahedral boron‐containing functional groups and their ligand electron delocalizing ability also play a critical role. These findings establish boron ligands as a useful dial for tuning reactivity at the α‐carbon. 

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4. Synthesis of Novel Multifunctional bora-Ibuprofen Derivatives

   https://doi.org/10.3390/inorganics11020070  

   Abeysinghe, Randika T.; Ravenscroft, Alexis C.; Knowlden, Steven W.; Akhmedov, Novruz G.; Dolinar, Brian S.; Popp, Brian V. (February 2023, Inorganics)

   A unique class of β-boron-functionalized non-steroidal anti-inflammatory compound (pinB-NSAID) was previously synthesized via copper-catalyzed 1,2-difunctionalization of the respective vinyl arene with CO2 and B2pin2 reagents. Here, pinacolylboron-functionalized ibuprofen (pinB-ibuprofen) was used as a model substrate to develop the conditions for pinacol deprotection and subsequent boron functionalization. Initial pinacol-boronic ester deprotection was achieved by transesterification with diethanolamine (DEA) from the boralactonate organic salt. The resulting DEA boronate adopts a spirocyclic boralactonate structure rather than a diazaborocane–DABO boronate structure. The subsequent acid-mediated hydrolysis of DEA and transesterification/transamination provided a diverse scope of new boron-containing ibuprofen derivatives. 

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5. Phosphonium Boranes for the Selective Transport of Fluoride Anions across Artificial Phospholipid Membranes

   https://doi.org/10.1002/anie.201914958  

   Park, Gyeongjin; Gabbaï, François P. (February 2020, Angewandte Chemie International Edition)

   Abstract With the view of developing selective transmembrane anion transporters, a series of phosphonium boranes of general formula [p‐RPh₂P(C₆H₄)BMes₂]⁺have been synthesized and evaluated. The results demonstrate that variation of the R group appended to the phosphorus atom informs the lipophilicity of these compounds, their Lewis acidity, as well as their transport activity. Anion transport experiments in POPC‐based large unilamellar vesicles show that these main‐group cations are highly selective for the fluoride anion, which is transported more than 20 times faster than the chloride anion. Finally, this work shows that the anion transport properties of these compounds are extremely sensitive to the steric crowding about the boron atom, pointing to the crucial involvement of the Group 13 element as the anion binding site. 

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