期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 20, 期 8, 页码 2215-2223出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201302967
关键词
alkynes; bifurcation; CH activation; density functional calculations; gold
资金
- Fonds der Chemischen Industrie
- Archimedes Foundation
- Ministry of Education and Research of Estonia
- Ministry for Education and Research
- Ministry for Science, Research and Arts Baden-Wurttemberg
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 compoundssubstrate classes unexplored to dateexhibiting 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of the cyclization mode in the bifurcated cyclization area demonstrated that classical transition-state theory is no longer valid to explain the high experimentally observed selectivity.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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