An Efficient Synthesis of Nitriles from Aldoximes in the Presence of Trifluoromethanesulfonic Anhydride in Mild Conditio
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n Efficient Synthesis of Nitriles from Aldoximes in the Presence of Trifluoromethanesulfonic Anhydride in Mild Conditions N. Uludaga,* a
Universirty of Namık Kemal, Faculty of Art and Sciences, Department of Chemistry, Tekirdag, 59030 Turkey e-mail: [email protected] Received March 26, 2020; revised April 4, 2020; accepted April 16, 2020
Abstract—A new and convenient protocol has been proposed for the transformation of aldoximes to nitriles using trifluoromethanesulfonic anhydride and triethylamine. The proposed method allows a range of aldoximes, including aromatic, heterocyclic, aliphatic, and cycloaliphatic aldoximes, to be converted to the corresponding nitriles in good to excellent yields. Keywords: aldoximes, nitriles, trifluoromethanesulfonic anhydride, dehydration
DOI: 10.1134/S1070428020090225 INTRODUCTION Substituted nitriles are key molecular scaffolds in the synthesis of many organic compounds [1–3]. Several routes for the synthesis of nitriles from aldoximes are important because nitriles are useful organic synthons in preparative organic chemistry; they can be converted into aldehydes, amides, ketones, carboxylic acids, and nitrogen-containing heterocycles [4, 5]. Yet the search for better reagents continues, generating interest methods for converting aldoximes to nitriles. Although many transformations have been reported [6–15], the development of more efficient methods for synthesizing nitriles remains a goal of the scientific community [16, 17]. Nitriles are the key constituents of many pharmacophores in commercially available drugs [18], and nitrile-containing pharmaceuticals have diverse medicinal indications. For example, entacopone is a vinylic nitrile prescribed for Parkinson’s disease [19], and finrozole is an approved drug used as a novel nonsteroidal inhibitor for the treatment of breast cancer [20]. The role of nitriles in synthetic chemistry highlights the importance of developing a fast, low-cost, facile, and feasible method for synthesizing various nitriles. A variety of techniques have been developed to synthesize nitriles from diverse aldoxime precursors [21–25]. Numerous reagents have been developed for this purpose, including FeCl3 [26], Na2SO3/SOCl2 [27], (1H-benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP), 1H-benzotri-
azol-1-yl 4-methylbenzenesulfonate (Bt-OTs) [28], P(RNCH2CH2)3N (proazaphosphatranes) [29], silicasupported thionyl chloride [30], N-hydroxyphthalimide [31], and (COCl)2 [32]. However, these reagents may have some limitations, including their high cost, scarcity, low yields, harsh reaction conditions, long reaction times, and work-up difficulties. Therefore, there is still a need to develop a better method for synthesizing nitriles. Trifluoromethanesulfonic anhydride was introduced for the use in synthesizing primary amides and their conversion into nitriles [33], although it has also been used in other important organic reactions [34, 35]. Our interest in nitrile chemistry led us to consider the use of triflic anhydride as an altern
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