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Boylan A, Nguyen TS, Lundy BJ, Li JY, Vallakati R, Sundstrom S, May JA. 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. Molecules 2021; 26:1615. [PMID: 33799473 PMCID: PMC8000498 DOI: 10.3390/molecules26061615] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 03/05/2021] [Accepted: 03/08/2021] [Indexed: 12/01/2022] Open
Abstract
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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Affiliation(s)
- Amy Boylan
- Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building 112, Houston, TX 77204-5003, USA; (A.B.); (T.S.N.); (B.J.L.); (J.-Y.L.); (R.V.); (S.S.)
| | - Thien S. Nguyen
- Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building 112, Houston, TX 77204-5003, USA; (A.B.); (T.S.N.); (B.J.L.); (J.-Y.L.); (R.V.); (S.S.)
- Graduate School of Energy, Environment, Water and Sustainability (EEWS), Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Korea
| | - Brian J. Lundy
- Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building 112, Houston, TX 77204-5003, USA; (A.B.); (T.S.N.); (B.J.L.); (J.-Y.L.); (R.V.); (S.S.)
- Baker Hughes, 17021 Aldine Westfield Rd, Houston, TX 77073, USA
| | - Jian-Yuan Li
- Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building 112, Houston, TX 77204-5003, USA; (A.B.); (T.S.N.); (B.J.L.); (J.-Y.L.); (R.V.); (S.S.)
- Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
| | - Ravikrishna Vallakati
- Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building 112, Houston, TX 77204-5003, USA; (A.B.); (T.S.N.); (B.J.L.); (J.-Y.L.); (R.V.); (S.S.)
- Vallark Pharma Pvt. Ltd., Genome Valley, Turkapally, Hyderabad 500078, India
| | - Sasha Sundstrom
- Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building 112, Houston, TX 77204-5003, USA; (A.B.); (T.S.N.); (B.J.L.); (J.-Y.L.); (R.V.); (S.S.)
- Department of Chemistry and Biochemistry, Baylor Sciences Bldg. D.208, One Bear Place #97348, Waco, TX 76798, USA
| | - Jeremy A. May
- Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building 112, Houston, TX 77204-5003, USA; (A.B.); (T.S.N.); (B.J.L.); (J.-Y.L.); (R.V.); (S.S.)
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