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Girvin ZC, Cotter LF, Yoon H, Chapman SJ, Mayer JM, Yoon TP, Miller SJ. Asymmetric Photochemical [2 + 2]-Cycloaddition of Acyclic Vinylpyridines through Ternary Complex Formation and an Uncontrolled Sensitization Mechanism. J Am Chem Soc 2022; 144:20109-20117. [PMID: 36264837 PMCID: PMC9633457 DOI: 10.1021/jacs.2c09690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Stereochemical control of photochemical reactions that occur via triplet energy transfer remains a challenge. Suppressing off-catalyst stereorandom reactivity is difficult for highly reactive open-shell intermediates. Strategies for suppressing racemate-producing, off-catalyst pathways have long focused on formation of ground state, substrate-catalyst chiral complexes that are primed for triplet energy transfer via a photocatalyst in contrast to their off-catalyst counterparts. Herein, we describe a strategy where both a chiral catalyst-associated vinylpyridine and a nonassociated, free vinylpyridine substrate can be sensitized by an Ir(III) photocatalyst, yet high levels of diastereo- and enantioselectivity in a [2 + 2] photocycloaddition are achieved through a preferred, highly organized transition state. This mechanistic paradigm is distinct from, yet complementary to current approaches for achieving high levels of stereocontrol in photochemical transformations.
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Affiliation(s)
- Zebediah C. Girvin
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Laura F. Cotter
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Hyung Yoon
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Steven J. Chapman
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
| | - Tehshik P. Yoon
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Scott J. Miller
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06511, United States
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Abstract
We experimentally discovered and theoretically analyzed a photochemical mechanism, which we term proton-coupled energy transfer (PCEnT). A series of anthracene-phenol-pyridine triads formed a local excited anthracene state after light excitation at a wavelength of ~400 nanometers (nm), which led to fluorescence around 550 nm from the phenol-pyridine unit. Direct excitation of phenol-pyridine would have required ~330-nm light, but the coupled proton transfer within the phenol-pyridine unit lowered its excited-state energy so that it could accept excitation energy from anthracene. Singlet-singlet energy transfer thus occurred despite the lack of spectral overlap between the anthracene fluorescence and the phenol-pyridine absorption. Moreover, theoretical calculations indicated negligible charge transfer between the anthracene and phenol-pyridine units. We construe PCEnT as an elementary reaction of possible relevance to biological systems and future photonic devices.
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Affiliation(s)
| | - Zhen Tao
- Yale University, Department of Chemistry, New Haven, Connecticut 06520, USA
| | - Giovanny A. Parada
- Yale University, Department of Chemistry, New Haven, Connecticut 06520, USA
- The College of New Jersey, Department of Chemistry, Ewing, NJ 08628, USA
| | - Laura F. Cotter
- Yale University, Department of Chemistry, New Haven, Connecticut 06520, USA
| | | | - James M. Mayer
- Yale University, Department of Chemistry, New Haven, Connecticut 06520, USA
| | - Leif Hammarström
- Uppsala University, Department of Chemistry, Ångström laboratory, Uppsala, Box 523, SE75120, Sweden
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Kazerouni AM, Brandes DS, Davies CC, Cotter LF, Mayer JM, Chen S, Ellman JA. Visible Light-Mediated, Highly Diastereoselective Epimerization of Lactams from the Most Accessible to the More Stable Stereoisomer. ACS Catal 2022; 12:7798-7803. [DOI: 10.1021/acscatal.2c02232] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Amaan M. Kazerouni
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Daniel S. Brandes
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Cassondra C. Davies
- Department of Chemistry and Biochemistry, Oberlin College, Oberlin, Ohio 44074, United States
| | - Laura F. Cotter
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Shuming Chen
- Department of Chemistry and Biochemistry, Oberlin College, Oberlin, Ohio 44074, United States
| | - Jonathan A. Ellman
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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Cotter LF, Brown PJ, Nelson RC, Takematsu K. Divergent Hammett Plots of the Ground- and Excited-State Proton Transfer Reactions of 7-Substituted-2-Naphthol Compounds. J Phys Chem B 2019; 123:4301-4310. [PMID: 31021637 DOI: 10.1021/acs.jpcb.9b01295] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The rational design of photoacids requires accessible predictive models of the electronic effect of functional groups on chemical templates of interest. Here, the effect of substituents on the photoacidity and excited-state proton transfer (PT) pathways of prototype 2-naphthol (2OH) at the symmetric C7 position was investigated through photochemical and computational studies of 7-amino-2-naphthol (7N2OH) and 7-methoxy-2-naphthol (7OMe2OH). Time-resolved emission experiments of 7N2OH revealed that the presence of an electron-withdrawing versus electron-donating group (EWG vs EDG, NH3+ vs NH2) led to a drastic decline in photoacidity: p Ka* = 1.1 ± 0.2 vs 9.6 ± 0.2. Time-dependent density functional theory calculations with explicit water molecules confirmed that the excited neutral state (x = NH2) is greatly stabilized by water, with equation-of-motion coupled cluster singles and doubles calculations supporting potential mixing between the La and Lb states. Similar suppression of photoacidity, however, was not observed for 7OMe2OH with EDG OCH3, p Ka* = 2.7 ± 0.1. Hammett plots of the ground- and excited-state PT reactions of substituted 7-x-2OH compounds (x = CN, NH3+, H, CH3, OCH3, OH, and NH2) vs Hammett parameters σp showed breaks in the linearity between the EDG and EWG regions: ρ ∼ 0 vs 1.14 and ρ* ∼ 0 vs 3.86. The divergent acidic behavior most likely arises from different mixing mechanisms of the lowest Lb state with the La and possible Bb states upon substitution of naphthalene in water.
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Affiliation(s)
- Laura F Cotter
- Department of Chemistry , Bowdoin College , Brunswick , Maine 04011 , United States
| | - Paige J Brown
- Department of Chemistry , Bowdoin College , Brunswick , Maine 04011 , United States
| | - Ryan C Nelson
- Department of Chemistry , Bowdoin College , Brunswick , Maine 04011 , United States
| | - Kana Takematsu
- Department of Chemistry , Bowdoin College , Brunswick , Maine 04011 , United States
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