title: Photoaddition reactions of acetylpyridines with silyl ketene acetals: SET vs [2 + 2]-cycloaddition pathways.
abstract: 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 β-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 β-hydroxyester forming, Claisen or Mukaiyama condensation reactions under mild conditions.
authors.affiliation: Department of Chemistry and Chemistry Institute for Functional Materials, Pusan National University, Busan 609-735, Korea.
authors.forename: Hea Jung
authors.initials: HJ
authors.lastname: Park
authors.forename: Ung Chan
authors.initials: UC
authors.lastname: Yoon
authors.forename: Hyang-Yeol
authors.initials: HY
authors.lastname: Lee
authors.forename: Dae Won
authors.initials: DW
authors.lastname: Cho
authors.forename: Dae Won
authors.initials: DW
authors.lastname: Cho
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Mariano
mesh_terms: D061565:Cycloaddition Reaction; D005030:Ethylenes / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D010777:Photochemistry; D011725:Pyridines / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*
chemical_list: D005030:Ethylenes; D007659:Ketones; D011725:Pyridines; D012821:Silanes; C008223:ketene