A Novel Route to 5-Substituted 3-Isoxazolols. Cyclization of <i>N,O-</i>DiBoc β-Keto Hydroxamic Acids Synthesized via Acyl Meldrum's Acids
作者:Ulrik S. Sørensen、Erik Falch、Povl Krogsgaard-Larsen
DOI:10.1021/jo991409d
日期:2000.2.1
We have found that N, O-diBoc-protected beta-keto hydroxamic acids can be synthesized and cyclized to 5-substituted 3-isoxazolols without formation of any byproduct. We present a novel and versatile three-step procedure in which carboxylic acid derivatives are converted into acyl Meldrum's acids which, upon aminolysis with N, O-bis(tert-butoxycarbonyl)hydroxylamine, lead to the N, O-diBoc-protected
3-异恶唑醇最通常由β-酮酯和羟胺合成。该环化通常产生主要副产物,相应的5-异恶唑酮。我们已经发现,可以合成N,O-diBoc保护的β-酮异羟肟酸并将其环化成5-取代的3-异恶唑醇,而不会形成任何副产物。我们提出了一种新颖且通用的三步程序,其中将羧酸衍生物转化为酰基麦德鲁姆酸,当与N,O-双(叔丁氧基羰基)羟胺进行氨解后,会生成N,O-diBoc保护的β-酮异羟肟酸。然后,将这些异羟肟酸类似物用盐酸处理后,环化成相应的5-取代的3-异恶唑醇。