Experimental and DFT Studies on Competitive Heterocyclic Rearrangements. 3. A Cascade Isoxazole−1,2,4-Oxadiazole−Oxazole Rearrangement

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• 作者：Andrea Pace ; Paola Pierro ; Silvestre Buscemi ; Nicolò ; Vivona ; Giampaolo Barone
• 刊名：Journal of Organic Chemistry
• 出版年：2009
• 出版时间：January 2, 2009
• 年：2009
• 卷：74
• 期：1
• 页码：351-358
• 全文大小：309K
• 年卷期：v.74,no.1(January 2, 2009)
• ISSN：1520-6904

文摘

The thermal rearrangements of 3-acylamino-5-methylisoxazoles 1 have been investigated under basic and neutral conditions and interpreted with the support of computational data. The density functional theory (DFT) study on the competitive routes available for the base-catalyzed thermal rearrangement of isoxazoles 1 showed that the Boulton−Katritzky (BK) rearrangement, producing the less stable 3-acetonyl-1,2,4-oxadiazoles 5, is a much more favored process than either the migration−nucleophilic attack−cyclization (MNAC) or the ring contraction−ring expansion (RCRE). In turn, an increase in reaction temperature will promote the MNAC of oxadiazoles 5, producing the more stable 2-acylaminooxazoles 8. The thermal rearrangement of 3-acylaminoisoxazoles 1 into oxazoles 8 can therefore be interpreted in terms of a cascade BK−MNAC rearrangement involving 3-acetonyl-1,2,4-oxadiazoles 5 as ancillary intermediates.