چاپ صفحه |  صفحه نخست سامانه |  نویسندگان |  اطلاعات تفضیلی |  دانلود مقاله | علوم پزشکی کرمانشاه |
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| هادی ادیبی | اول |
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| کلمات کلیدی | IRON(III) TRIFLUOROACETATE: CHEMOSELECTIVE AND RECYCLABLE LEWIS ACID CATALYST FOR THIOACETALIZATION AND TRANSTHIOACETALIZATION OF CARBONYL COMPOUNDS Adibi Hadi,* Samimi Heshmat Allah, and Jafari Hadi Department of Medicinal Chemistry, Faculty of Pharmacy, Kermanshah University of Medical Sciences, Kermanshah 67145-1673, IR Iran; Department of Chemistry, Faculty of Sciences, Guilan University, Rasht 41335-1914, IR Iran; Department of Chemistry, Islamic Azad University, Sanandaj Branch, Sanandaj, IR Iran E-mail: hadibi@kums.ac.ir Thioacetals are among carbonyl protecting groups, which their preparation is one of the major challenging problems during synthesis of multifunctional complex molecules.1 The importance of thioacetals is due in part to their inbuilt stability over usual acidic or basic conditions and also because of their behavior as masked acyl anions or methylene functions.2 Further, the use of thioacetals as blocking groups has enabled a new strategy for the electrophilic substitution on the carbonyl compound. In this view, there have been continued improvements in the methods of synthesis of thioacetals. Commonly, these compounds are prepared by condensation of carbonyl compounds with thiols or dithiols catalyzed by protic acids or Lewis acids.3 In recent years, modified reagents have also found recognizable importance.4 However, the developments in this area demand further searches for better catalysts that could be superior to the existing ones with regard to toxicity, handling, selectivity and recyclability. In this respect, we are interested to introduce efficient catalyst to overcome these limitations. Iron(III) trifluoroacetate [Fe(CF3CO2)3] was found to be recyclable, highly efficient and chemoselective Lewis acid catalyst for protection of a variety of carbonyl compounds as thioacetals under nearly neutral conditions. With the use of this catalyst, 1,3-dithiolanes and 1,3-dithianes were obtained in high yields from various aldehydes. Under the same conditions ketones were similarly but more slowly thioketalized. This difference in reactivity between aldehydes and ketones was successfully utilized for the thioacetalization of aldehydes in the presence of ketones and also for the chemoselective conversion of β-diketone into the corresponding dithioacetal. Transthioacetalization of O,O-acetals and O,O-ketals into cyclic thioacetals was also achieved by using this catalyst. Scheme 1 1. Kunz, H.; Waldmann, H. Comprehensive Organic Synthesis, Trost, B. M., Fleming, I., Eds.; Pergamon: New York, 1991; Vol. 6, pp 677–681. 2. (a) Page, P. C. B.; van Niel, M. B.; Prodger, J. Tetrahedron 1989, 45, 7643-7677; (b) Seebach, D. Angew. Chem., Int. Ed. Eng. 1979, 18, 239-258. 3. Green, T. W.; Wuts, P. G. M. Protective Groups in Organic Synthesis, John Wiley, New York, 2nd ed., 1991. 4. (a) Firouzabadi, H.; Iranpoor, N.; Karimi, B. Synthesis 1999, 58-60; (b) Firouzabadi, H.; Iranpoor, N.; Amani, K. Synthesis 2002, 59-62. |
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