More Like this

1. Accessing Ambiphilic Phosphine Boronates through C−H Borylation by an Unforeseen Cationic Iridium Complex

   https://doi.org/10.1002/anie.201812857  

   Wright, Shawn E.; Richardson‐Solorzano, Stephanie; Stewart, Tiffany N.; Miller, Christopher D.; Morris, Kelsey C.; Daley, Christopher J. A.; Clark, Timothy B. (January 2019, Angewandte Chemie International Edition)

   Abstract Ambiphilic molecules, which contain a Lewis base and Lewis acid, are of great interest based on their unique ability to activate small molecules. Phosphine boronates are one class of these substrates that have interesting catalytic activity. Direct access to these phosphine boronates is described through the iridium‐catalyzed C−H borylation of phosphines. An unconventional cationic iridium catalyst was identified as optimal for a range of phosphines, providing good yields and selectivity across a diverse class of phosphine boronates (isolated as the borane‐protected phosphine). A complimentary catalyst system (quinoline‐based silane ligand with [(COD)IrOMe]₂) was optimal for biphenyl‐based phosphines. Selective polyborylation was also shown providing bis‐ and tris‐borylated phosphines. Deprotection of the phosphine boronate provided free ambiphilic phosphine boronates, which do not have detectable interactions between the phosphorus and boron atoms in solution or the solid state. 

   more » « less
2. Strain-release 2-azaallyl anion addition/borylation of [1.1.1]propellane: synthesis and functionalization of benzylamine bicyclo[1.1.1]pentyl boronates

   https://doi.org/10.1039/D1SC01349A  

   Shelp, Russell A.; Ciro, Anthony; Pu, Youge; Merchant, Rohan R.; Hughes, Jonathan M.; Walsh, Patrick J. (May 2021, Chemical Science)

   null (Ed.)

   We report a 3-component reaction between N -benzyl ketimines, [1.1.1]propellane, and pinacol boronates to generate benzylamine bicyclo[1.1.1]pentane (BCP) pinacol boronates. These structures are analogous to highly sought diarylmethanamine cores, which are common motifs in bioactive molecules. We demonstrate the versatility of the boronate ester handle via downstream functionalization through a variety of reactions, including a challenging Pd-catalyzed (hetero)arylation that exhibits a broad substrate scope. Together, these methods enable the synthesis of high-value BCP benzylamines which are inaccessible by existing methods. Furthermore, we demonstrate the successful application of these newly developed (hetero)arylation conditions to a variety of challenging tertiary pinacol boronates, including nitrogen-containing heterocycles, 1,1-disubstituted cyclopropanes, and other BCP cores. 

   more » « less
3. C=O Scission and Reductive Coupling of Organic Carbonyls by a Redox-Active Diboraanthracene

   https://doi.org/10.1039/D0CC01142H  

   Taylor, Jordan; Harman, Hill (January 2020, Chemical Communications)

   The boron-centered reactivity of the diboraanthracene-auride complex ([Au(B2P2)][K(18-c-6)]; (B2P2, 9,10-bis(2-(diisopropylphosphino)- phenyl)-9,10-dihydroboranthrene) with a series of organic carbonyls is reported. The reaction of [(B2P2)Au]– with formaldehyde or paraformaldehyde results in a head-to-tail dimerization of two formaldehyde units across the boron centers. In contrast, the reaction of [(B2P2)Au]– with two equivalents of benzaldehyde yields the pinacol coupling product via C–C bond formation. Careful stoichiometric addition of one equivalent of benzaldehyde to [Au(B2P2)]– enabled the isolation of an adduct corresponding to the formal [4+2] cycloaddition of the C=O bond of benzaldehyde across the boron centers. This adduct reacts with a second equivalent of benzaldehyde to produce the pinacol coupling product. Finally, the reaction of [Au(B2P2)]– with acetone results in a formal reductive deoxygenation with discrete hydroxo and 2-propenyl units bound to the boron centers. This reaction is proposed to proceed via an analogous [4+2] cycloadduct, highlighting the unique small molecule activation chemistry available to this platform. 

   more » « less
4. Remote-Controlled Exchange Rates by Photoswitchable Internal Catalysis of Dynamic Covalent Bonds

   https://doi.org/10.1021/jacs.2c04658  

   Barsoum, David N.; Kirinda, Viraj C.; Kang, Boyeong; Kalow, Julia A. (May 2022, Journal of the American Chemical Society)

   The transesterification rate of boronate esters with diols is tunable over 14 orders of magnitude. Rate acceleration is achieved by internal base catalysis, which lowers the barrier for proton transfer. Here we report a photoswitchable internal catalyst that tunes the rate of boronic ester/diol exchange over 4 orders of magnitude. We employed an acylhydrazone molecular photoswitch, which forms a thermally stable but photoreversible intramolecular H-bond, to gate the activity of the internal base catalyst in 8-quinoline boronic ester. The photoswitch is bidirectional and can be cycled repeatedly. The intramolecular H-bond is found to be essential to the design of this photoswitchable internal catalyst, as protonating the quinoline with external sources of acid has little effect on the exchange rate. 

   more » « less
5. Photochemistry of N ‐Phenyl Dibenzothiophene Sulfoximine ^†

   https://doi.org/10.1111/php.13456  

   Isor, Ankita; Hommelsheim, Renè; Cone, Grant W.; Frings, Marcus; Petroff, II, John T.; Bolm, Carsten; McCulla, Ryan D. (June 2021, Photochemistry and Photobiology)

   Abstract Sulfoximines are popular scaffolds in drug discovery due to their hydrogen bonding properties and chemical stability. In recent years, the role of reactive intermediates such as nitrenes has been studied in the synthesis and degradation of sulfoximines. In this work, the photochemistry ofN‐phenyl dibenzothiophene sulfoximine [5‐(phenylimino)‐5H‐5λ⁴‐dibenzo[b,d]thiopheneS‐oxide] was analyzed. The structure resembles a combination ofN‐phenyl iminodibenzothiophene and dibenzothiopheneS‐oxide, which generate nitrene and O(³P) upon UV‐A irradiation, respectively. The photochemistry ofN‐phenyl dibenzothiophene sulfoximine was explored by monitoring the formation of azobenzene, a photoproduct of triplet nitrene, using direct irradiation and sensitized experiments. The reactivity profile was further studied through direct irradiation experiments in the presence of diethylamine (DEA) as a nucleophile. The studies demonstrated thatN‐phenyl dibenzothiophene sulfoximine underwent S–N photocleavage to release singlet phenyl nitrene which formed a mixture of azepines in the presence of DEA and generated moderate amounts of azobenzene in the absence of DEA to indicate formation of triplet phenyl nitrene. 

   more » « less