Evidence for involvement of cationic intermediate in epoxidation of chiral allylic alcohols and unfunctionalised alkenes catalysed by MnIII(quinazolinone) complexes |
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Authors: | Murat Çakıcı Hamdullah Kılıç Sabri Ulukanlı Duygu Ekinci |
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Affiliation: | 1. Chemistry Department, Faculty of Science, Atatürk University, 25240 Erzurum, Turkey;2. Chemistry Department, Faculty of Science and Letters, Osmaniye Korkut Ata University, 80000 Osmaniye, Turkey |
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Abstract: | A pair of MnIII(quinazolinone) complexes was prepared and evaluated in the catalytic epoxidation of the chiral allylic alcohols and unfunctionalised alkenes with iodosylbenzene. Epoxidation of chiral allylic alcohols with 1,3-allylic strain proceeded chemo- and diastereoselectively to give threo-epoxy alcohol (up to 99% d.r). Epoxidation of unfunctionalised alkenes by the proposed catalyst system proceeded nonselectively, as evidenced by the formation of isomerization and rearrangement products in the epoxidation of (Z)-stilbene. A three-step pathway involving a cationic intermediate is proposed for the formation of isomerization and rearrangement products. The fact that only products resulting from the cationic intermediate were detected in the oxidation of a mechanistic probe, (2-methoxy-3-vinylcyclopropyl)benzene, with MnIII(quinazolinone) and PhIO substantiated the cationic oxygen transfer mechanism. |
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Keywords: | Allylic compounds Manganese Quinazolinone Catalysis Epoxidation Chemoselectivity Diastereoselectivity Reaction mechanisms |
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