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LaPorte AJ, Feldner JE, Spies JC, Maher TJ, Burke MD. MIDA- and TIDA-Boronates Stabilize α-Radicals Through B-N Hyperconjugation. Angew Chem Int Ed Engl 2023; 62:e202309566. [PMID: 37540542 DOI: 10.1002/anie.202309566] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 08/03/2023] [Accepted: 08/04/2023] [Indexed: 08/05/2023]
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 σB-N hyperconjugation 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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Affiliation(s)
- Antonio J LaPorte
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
| | - Jack E Feldner
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
| | - Jan C Spies
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
| | - Tom J Maher
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
| | - Martin D Burke
- Department of Chemistry, University of Illinois, Urbana, IL, 61820, USA
- Carle Illinois College of Medicine, University of Illinois, Urbana, IL, 61820, USA
- Department of Biochemistry, University of Illinois, Urbana, IL, 61820, USA
- Arnold and Mable Beckman Institute, University of Illinois, Urbana, IL, 61820, USA
- Carl R. Woese Institute for Genomic Biology, University of Illinois, Urbana, IL, 61820, USA
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2
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Blair DJ, Chitti S, Trobe M, Kostyra DM, Haley HMS, Hansen RL, Ballmer SG, Woods TJ, Wang W, Mubayi V, Schmidt MJ, Pipal RW, Morehouse GF, Palazzolo Ray AME, Gray DL, Gill AL, Burke MD. Automated iterative Csp 3-C bond formation. Nature 2022; 604:92-97. [PMID: 35134814 PMCID: PMC10500635 DOI: 10.1038/s41586-022-04491-w] [Citation(s) in RCA: 38] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 01/28/2022] [Indexed: 11/09/2022]
Abstract
Fully automated synthetic chemistry would substantially change the field by providing broad on-demand access to small molecules. However, the reactions that can be run autonomously are still limited. Automating the stereospecific assembly of Csp3-C bonds would expand access to many important types of functional organic molecules1. Previously, methyliminodiacetic acid (MIDA) boronates were used to orchestrate the formation of Csp2-Csp2 bonds and were effective building blocks for automating the synthesis of many small molecules2, but they are incompatible with stereospecific Csp3-Csp2 and Csp3-Csp3 bond-forming reactions3-10. Here we report that hyperconjugative and steric tuning provide a new class of tetramethyl N-methyliminodiacetic acid (TIDA) boronates that are stable to these conditions. Charge density analysis11-13 revealed that redistribution of electron density increases covalency of the N-B bond and thereby attenuates its hydrolysis. Complementary steric shielding of carbonyl π-faces decreases reactivity towards nucleophilic reagents. The unique features of the iminodiacetic acid cage2, which are essential for generalized automated synthesis, are retained by TIDA boronates. This enabled Csp3 boronate building blocks to be assembled using automated synthesis, including the preparation of natural products through automated stereospecific Csp3-Csp2 and Csp3-Csp3 bond formation. These findings will enable increasingly complex Csp3-rich small molecules to be accessed via automated assembly.
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Affiliation(s)
- Daniel J Blair
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
| | - Sriyankari Chitti
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Melanie Trobe
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - David M Kostyra
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Hannah M S Haley
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Richard L Hansen
- Department of Chemistry, REVOLUTION Medicines, Inc., Redwood City, CA, USA
| | - Steve G Ballmer
- Department of Chemistry, REVOLUTION Medicines, Inc., Redwood City, CA, USA
| | - Toby J Woods
- George L. Clark X-Ray Facility and 3M Materials Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Wesley Wang
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Vikram Mubayi
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Michael J Schmidt
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Robert W Pipal
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Greg F Morehouse
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Andrea M E Palazzolo Ray
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Danielle L Gray
- George L. Clark X-Ray Facility and 3M Materials Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Adrian L Gill
- Department of Chemistry, REVOLUTION Medicines, Inc., Redwood City, CA, USA
| | - Martin D Burke
- Roger Adams Laboratory, School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
- Carle Illinois College of Medicine, Urbana, IL, USA.
- Arnold and Mabel Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
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Li Y, Wang J, Wang Z, Huang M, Yan B, Cui X, Wu Y, Wu Y. Palladacycle-catalyzed Suzuki–Miyaura reaction of aryl/heteroaryl halides with MIDA boronates in EtOH/H2O or H2O. RSC Adv 2014. [DOI: 10.1039/c4ra07486f] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
With good to excellent yields, a series of mono- or diheteroaryl compounds were synthesized via the palladacycle-catalyzed Suzuki–Miyaura reaction of various N-methyliminodiacetic acid (MIDA) boronates with aryl/heteroaryl halides in EtOH/H2O or H2O.
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Affiliation(s)
- Yabo Li
- College of Chemistry and Molecular Engineering
- Henan Key Laboratory of Chemical Biology and Organic Chemistry
- Key Laboratory of Applied Chemistry of Henan Universities
- Zhengzhou University
- Zhengzhou, P. R. China
| | - Jingran Wang
- College of Chemistry and Molecular Engineering
- Henan Key Laboratory of Chemical Biology and Organic Chemistry
- Key Laboratory of Applied Chemistry of Henan Universities
- Zhengzhou University
- Zhengzhou, P. R. China
| | - Zhiwei Wang
- College of Chemistry and Molecular Engineering
- Henan Key Laboratory of Chemical Biology and Organic Chemistry
- Key Laboratory of Applied Chemistry of Henan Universities
- Zhengzhou University
- Zhengzhou, P. R. China
| | - Mengmeng Huang
- College of Chemistry and Molecular Engineering
- Henan Key Laboratory of Chemical Biology and Organic Chemistry
- Key Laboratory of Applied Chemistry of Henan Universities
- Zhengzhou University
- Zhengzhou, P. R. China
| | - Beiqi Yan
- College of Chemistry and Molecular Engineering
- Henan Key Laboratory of Chemical Biology and Organic Chemistry
- Key Laboratory of Applied Chemistry of Henan Universities
- Zhengzhou University
- Zhengzhou, P. R. China
| | - Xiuling Cui
- College of Chemistry and Molecular Engineering
- Henan Key Laboratory of Chemical Biology and Organic Chemistry
- Key Laboratory of Applied Chemistry of Henan Universities
- Zhengzhou University
- Zhengzhou, P. R. China
| | - Yusheng Wu
- College of Chemistry and Molecular Engineering
- Henan Key Laboratory of Chemical Biology and Organic Chemistry
- Key Laboratory of Applied Chemistry of Henan Universities
- Zhengzhou University
- Zhengzhou, P. R. China
| | - Yangjie Wu
- College of Chemistry and Molecular Engineering
- Henan Key Laboratory of Chemical Biology and Organic Chemistry
- Key Laboratory of Applied Chemistry of Henan Universities
- Zhengzhou University
- Zhengzhou, P. R. China
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New strategy to the synthesis of (N→B) phenyl[N-alkyliminodiacetate-O,O′,N]boranes: The crystal structure of (N→B) phenyl[N-benzyliminodiacetate-O,O′,N]borane, (N→B)phenyl[N-(4-methyl)benzyliminodiacetate-O,O′,N]borane and (N→B) phenyl[N-phenacyliminodiacetate-O,O′,N]borane. Polyhedron 2009. [DOI: 10.1016/j.poly.2009.05.043] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Abstract
Due to its sensitivity to most synthetic reagents, it is typically necessary to introduce the boronic acid functional group just prior to its utilization. Overcoming this important limitation, we herein report that air- and chromatographically stable MIDA boronates are compatible with a wide range of common reagents which enables the multistep synthesis of complex boronic acid building blocks from simple B-containing starting materials. X-ray and variable temperature NMR studies link the unique stability of MIDA boronates to a kinetic inaccessibility of the potentially reactive boron p-orbital and/or nitrogen lone pair. These findings were collectively harnessed to achieve a short and modular total synthesis of (+)-crocacin C via the iterative cross-coupling of a structurally complex, MIDA-protected haloboronic acid building block.
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Affiliation(s)
- Eric P Gillis
- Roger Adams Laboratory, Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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11
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Diastereoselective Synthesis of β-Hydroxyketones. Nat Prod Commun 2008. [DOI: 10.1177/1934578x0800300305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The diastereoselective synthesis of 2,4-dibromo-3-hydroxy-1,3-diphenylbutan-1-one [4(a-a’)]; 2,4-dibromo-3-hydroxy-1,3-di [( p-chloro)phenyl]butan-1-one [5(a-a’)] and 2,4-dibromo-3-hydroxy-1,3-di[( p-phenyl)phenyl]butan-1-one [6(a-a’)] using (N→B) phenyl( N-methyliminodiacetate- O,O',N)borane and n-BuLi is reported. The mixture of these compounds was characterized by1H,13C NMR, HETCOR, COSY and infrared spectroscopy and mass spectrometry.
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