Padwa Albert, Rashatasakhon Paitoon, Rose Mickea
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Org Chem. 2003 Jun 27;68(13):5139-46. doi: 10.1021/jo0341970.
The reaction of alpha-angelica lactone with alkylamines under aqueous conditions afforded 5-hydroxy-5-methylpyrrolidinones in high yield. When the reaction was carried out under anhydrous conditions, the only products obtained were the corresponding 4-oxopentanoic acid amides. Treatment of either class of compound with triflic anhydride (Tf(2)O) in pyridine resulted in the formation of various substituted sulfonamidofurans. The suggested mechanism involves initial formation of an iminium ion which is subsequently transformed into a transient imino triflate. Cyclization of the highly electrophilic imine onto the oxygen atom of the adjacent carbonyl group generates an imino dihydrofuran intermediate. This species reacts further with another equivalent of Tf(2)O to give the observed product. The nature of the Lewis acid used was found to affect the outcome of the cyclization reaction. In certain cases, the sulfonamide furan was utilized as a cycloaddition substrate for the synthesis of indolines and related heterocyclic systems.
在水相条件下，α-当归内酯与烷基胺反应可高产率地得到5-羟基-5-甲基吡咯烷酮。当反应在无水条件下进行时，得到的唯一产物是相应的4-氧代戊酸酰胺。在吡啶中用三氟甲磺酸酐（Tf(2)O）处理这两类化合物中的任何一种，都会导致形成各种取代的磺酰胺基呋喃。提出的机理涉及最初形成亚胺离子，该亚胺离子随后转化为瞬态亚胺三氟甲磺酸酯。高亲电亚胺环化到相邻羰基的氧原子上生成亚胺二氢呋喃中间体。该物种进一步与另一当量的Tf(2)O反应，得到观察到的产物。发现所用路易斯酸的性质会影响环化反应的结果。在某些情况下，磺酰胺呋喃被用作环加成底物来合成吲哚啉和相关的杂环体系。
