Photoaddition Reactions of Acetylpyridines with Silyl Ketene Acetals: SET vs [2+2]-Cycloaddition Pathways
- Photoaddition Reactions of Acetylpyridines with Silyl Ketene Acetals: SET vs [2+2]-Cycloaddition Pathways
- 조대원; 박혜정[박혜정]; 윤웅찬[윤웅찬]; 이향렬[이향렬]; 조대원; Patrick Mariano[Patrick Mariano]
- SINGLE-ELECTRON-TRANSFER; AROMATIC CARBONYL-COMPOUNDS; PHOTOCYCLIZATION REACTIONS; SUBSTITUTED PYRIDINES; MICHAEL REACTIONS; ORGANIC-SYNTHESIS; CATION RADICALS; CROWN-ETHERS; RICH ALKENES; ALLYLSILANES
- Issue Date
- AMER CHEMICAL SOC
- JOURNAL OF ORGANIC CHEMISTRY, v.77, no.22, pp.10304 - 10313
- Photoaddition reactions of silyl ketene acetals with 2-, 3- and 4-acetylpyridine have been explored. The results show that the acetylpyridines react with an electron rich, dimethyl-substituted silyl ketene acetal via a pathway in which excited state single electron transfer (SET) takes place to produce beta-hydroxyesters in high yields. In contrast, photochemical reactions of the acetylpyridines with an electron deficient, nonmethyl-substituted silyl ketene acetal generate oxetanes as major products, which arise via a route involving excited state [2 + 2]-cycloaddition. In addition, an increase in solvent polarity significantly enhances the relative efficiencies of the SET processes versus [2 + 2]-cycloaddition reactions. Importantly, the carbonyl groups rather than the pyridine moieties in the acetylpyridine substrates participate in both types of addition reactions. Finally, the results demonstrate that photoinduced electron transfer (PET)-promoted chemical reactions between acetylpyridines and electron rich silyl ketene acetals in polar solvent serve as useful methods to promote beta-hydroxyester forming, Claisen or Mukaiyama condensation reactions under mild conditions.
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