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Ma P, Svatunek D, Zhu Z, Boger DL, Duan XH, Houk KN. Computational Studies of Reactions of 1,2,4,5-Tetrazines with Enamines in MeOH and HFIP. J Am Chem Soc 2024. [PMID: 38941192 DOI: 10.1021/jacs.4c06067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/30/2024]
Abstract
The reaction between 1,2,4,5-tetrazines and alkenes in polar solvents proceeds through a Diels-Alder cycloaddition along the C-C axis (C3/C6 cycloaddition) of the tetrazine, followed by dinitrogen loss. By contrast, the reactions of 1,2,4,5-tetrazines with enamines in hexafluoroisopropanol (HFIP) give 1,2,4-triazine products stemming from a formal Diels-Alder addition across the N-N axis (N1/N4 cycloaddition). We explored the mechanism of this interesting solvent effect through DFT calculations in detail and revealed a novel reaction pathway characterized by C-N bond formation, deprotonation, and a 3,3-sigmatropic rearrangement. The participation of an HFIP molecule was found to be crucial to the N1/N4 selectivity over C3/C6 due to the more favored initial C-N bond formation than C-C bond formation.
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Affiliation(s)
- Pengchen Ma
- Department of Chemistry, School of Chemistry, Xi'an Key Laboratory of Sustainable Energy Material Chemistry and Engineering Research Center of Energy Storage Materials and Devices, Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
| | - Dennis Svatunek
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
- Institute of Applied Synthetic Chemistry, TU Wien, 1060 Vienna, Austria
| | - Zixi Zhu
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Dale L Boger
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Xin-Hua Duan
- Department of Chemistry, School of Chemistry, Xi'an Key Laboratory of Sustainable Energy Material Chemistry and Engineering Research Center of Energy Storage Materials and Devices, Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
| | - K N Houk
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States
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Sarkar B, Hajra A. Hydro-phosphorothiolation of Styrene and Cyclopropane with S-Hydrogen Phosphorothioates under Ambient Conditions. Org Lett 2024; 26:5141-5145. [PMID: 38848455 DOI: 10.1021/acs.orglett.4c01586] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2024]
Abstract
A metal-free hexafluoroisopropanol-mediated hydro-phosphorothiolation of styrenes and donor-acceptor cyclopropanes with S-hydrogen phosphorothioates in a Markovnikov fashion has been developed under ambient reaction conditions to afford a library of S-alkyl phosphorothioates. Notably, this strategy provides a simple and efficient way to produce biologically significant kitazin and iprobenfos derivatives. Mechanistic studies disclose that the reaction proceeds through a carbocation intermediate.
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Affiliation(s)
- Biswajit Sarkar
- Department of Chemistry, Visva-Bharati (A Central University), Santiniketan 731235, India
| | - Alakananda Hajra
- Department of Chemistry, Visva-Bharati (A Central University), Santiniketan 731235, India
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Saha J, Banerjee S, Malo S, Das AK, Das I. A Torquoselective Thermal 6π-Electrocyclization Approach to 1,4-Cyclohexadienes via Solvent-Aided Proton Transfer: Experimental and Theoretical Studies. Chemistry 2024; 30:e202304009. [PMID: 38179806 DOI: 10.1002/chem.202304009] [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: 12/01/2023] [Revised: 12/26/2023] [Accepted: 01/05/2024] [Indexed: 01/06/2024]
Abstract
The thermal 6π-electrocyclization of hexatriene typically delivers 1,3-cyclohexadiene (1,3-CHD). However, there is only limited success in directly synthesizing 1,4-cyclohexadiene (1,4-CHD) using such an approach, probably due to the difficulty in realizing thermally-forbidden 1,3-hydride shift after electrocyclic ring closure. The present study shows that by heating (2E,4E,6E)-hexatrienes bearing ester or ketone substituents at the C1-position in a mixture of toluene/MeOH or EtOH (2 : 1) solvents at 90-100 °C, 1,4-CHDs can be selectively synthesized. This is achieved through a torquoselective disrotatory 6π-electrocyclic ring closure followed by a proton-transfer process. The success of this method depends on the polar protic solvent-assisted intramolecular proton transfer from 1,3-CHD to 1,4-CHD, which has been confirmed by deuterium-labeling experiments. There are no reports to date for such a solvent-assisted isomerization. Density functional theory (DFT) studies have suggested that forming 1,3-CHD and subsequent isomerization is a thermodynamically feasible process, regardless of the functional groups involved. Two possible successive polar solvent-assisted proton-transfer pathways have been identified for isomerization.
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Affiliation(s)
- Jayanta Saha
- Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical BiologyJadavpur, Kolkata, 700032, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | - Soumadip Banerjee
- School of Mathematical and Computational Sciences, Indian Association for the Cultivation of Science Jadavpur, Kolkata, 700032, India
| | - Sidhartha Malo
- Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical BiologyJadavpur, Kolkata, 700032, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | - Abhijit Kumar Das
- School of Mathematical and Computational Sciences, Indian Association for the Cultivation of Science Jadavpur, Kolkata, 700032, India
| | - Indrajit Das
- Organic and Medicinal Chemistry Division, CSIR-Indian Institute of Chemical BiologyJadavpur, Kolkata, 700032, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
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