Gold-catalyzed cyclization of diynes: controlling the mode of 5-endo versus 6-endo cyclization$dan experimental and theoretical study by utilizing diethynylthiophenes
Herein, a dual-gold catalyzed cyclization of 3,4-diethynylthiophenes generating pentaleno[c]thiophenes through gold-vinylidenes and CH bond activation is disclosed. Various new heteroaromatic compounds—substrate classes unexplored to date—exhibiting three five-membered annulated ring systems could...
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| Main Authors: | , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
16 January 2014
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| In: |
Chemistry - a European journal
Year: 2014, Volume: 20, Issue: 8, Pages: 2215-2223 |
| ISSN: | 1521-3765 |
| DOI: | 10.1002/chem.201302967 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1002/chem.201302967 Verlag, lizenzpflichtig, Volltext: https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.201302967 
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| Author Notes: | Max M. Hansmann, Svetlana Tšupova, Matthias Rudolph, Frank Rominger, A. Stephen K. Hashmi |
| Summary: | Herein, a dual-gold catalyzed cyclization of 3,4-diethynylthiophenes generating pentaleno[c]thiophenes through gold-vinylidenes and CH bond activation is disclosed. Various new heteroaromatic compounds—substrate classes unexplored to date—exhibiting three five-membered annulated ring systems could be synthesized in moderate to high yields. By comparison of the solid-state structures of the corresponding gold-acetylides, it could be demonstrated that the cyclization mode (5-endo versus 6-endo) is controlled by the electronic and not steric nature of the diyne backbone. Depending on different backbones, we calculated thermodynamic stabilities and full potential-energy surfaces giving insight into the crucial dual-activation cyclization step. In the case of the 3,4-thiophene backbone, in which the initial cyclization is rate and selectivity determining, two energetically distinct transition states could be localized explaining the observed 5-endo cyclization mode by classical transition-state theory. In the case of vinyl and 2,3-thiophene backbones, the theoretical analysis of the cyclization mode in the bifurcated cyclization area demonstrated that classical transition-state theory is no longer valid to explain the high experimentally observed selectivity. Herein, for the first time, the influence of the backbone and the aromatic stabilization effect of the 6-endo product in the crucial cyclization step could be visualized and quantified by calculating and comparing the full potential-energy surfaces. |
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| Item Description: | Gesehen am 24.09.2020 |
| Physical Description: | Online Resource |
| ISSN: | 1521-3765 |
| DOI: | 10.1002/chem.201302967 |