Construction of 3,5-substituted 1,2,4-oxadiazole rings triggered by tetrabutylammonium hydroxide: a highly efficient and fluoride-free ring closure reaction of O-acylamidoximes |
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Authors: | Hiromichi Otaka Junya IkedaDaisuke Tanaka Masanori Tobe |
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Institution: | Dainippon Sumitomo Pharma Co., Ltd, Enoki 33-94, Suita, Osaka 564-0053, Japan |
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Abstract: | Tetrabutylammonium hydroxide (TBAH) is an efficient and mild alternative to tetrabutylammonium fluoride (TBAF) for base catalyzed cyclizations of 1,2,4-oxadiazoles from O-acylamidoximes. For most 3,5-substituted 1,2,4-oxadiazoles the reactions were dramatically accelerated by addition of 0.1 equiv of TBAH at room temperature. This method was also more generally applicable allowing for a wider range of substrates. Additionally, due to the absence of fluoride, TBAH will not result in corrosion of reactor vessels and therefore is better suited for large-scale synthesis. |
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Keywords: | 1 2 4-Oxadiazole O-Acylamidoxime Tetrabutylammonium hydroxide Tetrabutylammonium fluoride |
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