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Gold-catalyzed cyclization of diynes: controlling the mode of 5-endo versus 6-endo cyclization--an experimental and theoretical study by utilizing diethynylthiophenes.
- Source :
-
Chemistry (Weinheim an der Bergstrasse, Germany) [Chemistry] 2014 Feb 17; Vol. 20 (8), pp. 2215-23. Date of Electronic Publication: 2014 Jan 16. - Publication Year :
- 2014
-
Abstract
- Herein, a dual-gold catalyzed cyclization of 3,4-diethynylthiophenes generating pentaleno[c]thiophenes through gold-vinylidenes and C-H 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of the cyclization mode in the bifurcated cyclization area demonstrated that classical transition-state theory is no longer valid to explain the high experimentally observed selectivity.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.<br /> (Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)
Details
- Language :
- English
- ISSN :
- 1521-3765
- Volume :
- 20
- Issue :
- 8
- Database :
- MEDLINE
- Journal :
- Chemistry (Weinheim an der Bergstrasse, Germany)
- Publication Type :
- Academic Journal
- Accession number :
- 24436306
- Full Text :
- https://doi.org/10.1002/chem.201302967