G. Hughes
Ethynyl pi-extended 2,5-diphenyl-1,3,4-oxadiazoles and 2-phenyl 5-(2-thienyl)-1,3,4-oxadiazoles: synthesis, X-ray crystal structures and optical properties
Hughes, G.; Kreher, D.; Wang, C.S.; Batsanov, A.S.; Bryce, M.R.
Abstract
2-(4-tert-Butylphenyl)-5-(4-ethynylphenyl)-1,3,4-oxadiazole 1 reacts with a series of heteroaryl iodides under standard Sonogashira cross-coupling conditions (Pd[PPh3](2)Cl-2, CuI, triethylamine, THF) to yield products 2a-g in 40-79% yields (heteroaryl = 2- pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrazyl, 5-bromo-2-pyrimidyl, 2-thienyl and 3-thienyl, respectively). Compound 2f was lithiated followed by electrophilic iodination ( BuLi, perfluorohexyl iodide) to give 3, which by a two-step sequence gave the terminal ethynylthienyl derivative 5. Conversion of 5 into the terminal ethynylaldehyde derivative 7, via acetal derivative 6, proceeded in high yield. Starting from 2-iodo-5-methoxy-carbonylthiophene, a five-step sequence afforded 2-(4-tert-butylphenyl)-5-(4-ethynylthienyl)-1,3,4-oxadiazole 13 (13% overall yield). Reactions of 13 gave terminal pyridyl, pyrazyl, pyrimidyl and thienyl derivatives, analogous to those obtained from 1. Two-fold reaction of 13 with 2,5-diiodothiophene gave the bis(ethynylthienyl)thiophene derivative 15 (30% yield). Solution UV-Vis absorption and photoluminescence spectra establish that replacement of the phenyl ring in the 2,5-diphenyl-1,3,4-oxadiazole series 2a-g by a thienyl ring [i.e. the 2-phenyl-5-(2-thienyl)-1,3,4-oxadiazole series 14a-g] leads to a red shift in the lowest energy band in both the absorption spectra and emission spectra. The X-ray crystal structures of compounds 2d, 2g, 5 and 14d.CHCl3 reveal that the molecular structures are approximately planar although there are substantial differences in the conformations.
Citation
Hughes, G., Kreher, D., Wang, C., Batsanov, A., & Bryce, M. (2004). Ethynyl pi-extended 2,5-diphenyl-1,3,4-oxadiazoles and 2-phenyl 5-(2-thienyl)-1,3,4-oxadiazoles: synthesis, X-ray crystal structures and optical properties. Organic and Biomolecular Chemistry, 2(22), 3363-3367
Journal Article Type | Article |
---|---|
Publication Date | 2004 |
Journal | Organic and Biomolecular Chemistry |
Print ISSN | 1477-0520 |
Electronic ISSN | 1477-0539 |
Publisher | Royal Society of Chemistry |
Peer Reviewed | Peer Reviewed |
Volume | 2 |
Issue | 22 |
Pages | 3363-3367 |
Public URL | https://durham-repository.worktribe.com/output/1569805 |
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