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1. Rate Dependence on Inductive and Resonance Effects for the Organocatalyzed Enantioselective Conjugate Addition of Alkenyl and Alkynyl Boronic Acids to β-Indolyl Enones and β-Pyrrolyl Enones

   https://doi.org/10.3390/molecules26061615  

   Boylan, Amy; Nguyen, Thien S.; Lundy, Brian J.; Li, Jian-Yuan; Vallakati, Ravikrishna; Sundstrom, Sasha; May, Jeremy A. (March 2021, Molecules)

   null (Ed.)

   Two key factors bear on reaction rates for the conjugate addition of alkenyl boronic acids to heteroaryl-appended enones: the proximity of inductively electron-withdrawing heteroatoms to the site of bond formation and the resonance contribution of available heteroatom lone pairs to stabilize the developing positive charge at the enone β-position. For the former, the closer the heteroatom is to the enone β-carbon, the faster the reaction. For the latter, greater resonance stabilization of the benzylic cationic charge accelerates the reaction. Thus, reaction rates are increased by the closer proximity of inductive electron-withdrawing elements, but if resonance effects are involved, then increased rates are observed with electron-donating ability. Evidence for these trends in isomeric substrates is presented, and the application of these insights has allowed for reaction conditions that provide improved reactivity with previously problematic substrates. 

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2. 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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3. High‐fidelity Recognition of Organotrifluoroborate Anions (R−BF ₃ ⁻ ) as Designer Guest Molecules

   https://doi.org/10.1002/chem.202201584  

   Sheetz, Edward_G; Zhang, Zhao; Marogil, Alyssa; Che, Minwei; Pink, Maren; Carta, Veronica; Raghavachari, Krishnan; Flood, Amar_H (August 2022, Chemistry – A European Journal)

   Abstract The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF₃⁻). We are exploring the development of these and other designer anions as anion‐recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF₃⁻, by cyanostar macrocycles that are size‐complementary to the inorganic BF₄⁻progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K⁺salts of R−BF₃⁻anions. 

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4. Chemical Modification of Silk Proteins via Palladium‐Mediated Suzuki−Miyaura Reactions

   https://doi.org/10.1002/macp.202300307  

   Santen, Racine M.; Owens, Kayla M.; Echague, Keith C.; Murphy, Amanda R. (October 2023, Macromolecular Chemistry and Physics)

   Abstract Suzuki−Miyaura cross‐coupling reactions are used to modify the tyrosine residues onBombyx morisilkworm silk proteins using a water‐soluble palladium catalyst. First, model reactions using tyrosine derivatives are screened to determine optimal reaction conditions. For these reactions, a variety of aryl boronic acids, solvents, buffers, and temperature ranges are explored. Qualitative information on the reaction progress is collected via high‐performance liquid chromatography (HPLC), mass spectrometry (MS), and nuclear magnetic resonance (NMR). Optimized reactions are then applied to silk proteins. It is demonstrated the ability to modify silk fibroin in solution by first iodinating the tyrosine residues on the protein, and then carrying out Suzuki‐Miyaura reactions with a variety of boronic acid derivatives. Modification of silk is confirmed with NMR, ion‐exchange chromatography (IEC), UV‐vis, and infrared spectroscopy (IR). 

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5. Synthesis of Dihydropyrazoles via Palladium‐Catalyzed Cascade Heterocyclization/Carbonylation/Arylation of β,γ‐Unsaturated N ‐Tosyl Hydrazones

   https://doi.org/10.1002/adsc.202301326  

   Dantas, Juliana_A; Hardy, Melissa_A; Costa, Mateus_O; De_Oliveira, Camila_P; Cabral, Tadeu_L_G; Tormena, Claudio_Francisco; Sigman, Matthew_S; Ferreira, Marco_A_B (December 2023, Advanced Synthesis & Catalysis)

   Abstract A Pd‐catalyzed heterocyclization/carbonylation/arylation cascade reaction between β,γ‐unsaturated N−Ts hydrazones and commercially available arylboronic acids as coupling partners is described, producing 2‐pyrazoline‐ketone derivatives in 11–78% yield. A detailed statistical analysis of reactivity patterns of boronic acids provided key information about the limitations of the method, highlighting the challenges of degradation pathways. Our methodology offers a tool for synthesizing diverse 2‐pyrazoline‐ketone derivatives, expanding the toolbox of accessible N−N‐heterocycles. 

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