The chemistry of zerumbone. Part 5: Structural transformation of the dimethylamine derivatives |
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Authors: | Takashi Kitayama Taketo YokoiYasushi Kawai Richard K HillMasanori Morita Tadashi OkamotoYukio Yamamoto Valery V FokinKBarry Sharpless Seiji Sawada |
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Institution: | a Department of Agricultural Chemistry, Faculty of Agriculture, Kinki University, Nara 631-8505, Japan b Kyoto University of Education, Fushimi, Kyoto 612-8522, Japan c Institute for Chemical Research, Kyoto University, Uji 611-0011, Japan d Department of Chemistry, University of Georgia, Athens, GA 30602, USA e Joint Center, Kinki University, Nara 631-8505, Japan f Graduate School of Human and Environmental Studies, Kyoto University, Sakyo, Kyoto 606-8501, Japan g Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037, USA |
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Abstract: | Zerumbone (1) and its 6,7-epoxide (2) react with ammonia and dimethylamine regio- and stereospecifically, affording monoamines 3, 4, 7 and 8. All adducts have the same relative configuration at C2 and C3. The conjugate amination is thermodynamically controlled to arrive at a single diastereomer. At 15°C 7 reacts with cyanide to give aminonitrile 10 as the single product, while at 30°C, acyclic aminonitrile 11 is also formed. The reaction with 8 affords at 0°C bicyclic aminonitrile 12 of the asteriscane skeleton, while at 30°C or higher temperature, mixtures of 12 and tricyclic nitriles 13 and 13′ are obtained. Refluxing of 7, 8 and 10 in aqueous acetonitrile promotes scission of the zerumbone ring by retro-Mannich reaction to provide acyclic aldehydes 16-18, respectively. The dimethylamino group of 7, 8 and 10 is eliminated stereospecifically by Cope- and base-catalyzed eliminations to regenerate the zerumbone skeleton in the products 1, 2 and 21. Cope elimination of 12 results in a mixture of 13 and 13′ by deaminative transannular etherification. |
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Keywords: | zerumbone sesquiterpene retro-Mannich asteriscane transannular Cope elimination |
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