C-Glycosides by Aqueous Condensation of β-Dicarbonyl Compounds with Unprotected Sugars
作者:I. Riemann、W.-D. Fessner、M. A. Papadopoulos、M. Knorst
DOI:10.1071/ch02012
日期:——
water, under mildly alkaline conditions, provides a�convenient and effective route to C-glycosidic ketones in high yields. Reactions usually proceed with high β`anomeric' stereoselectivity because product composition is determined by thermodynamic control. Mechanistically, the condensation follows a typical Knoevenagel scheme, after which an intramolecular oxa-Michael cyclization determines C-glycoside
在弱碱性条件下,1,3-二酮与未受保护的醛糖在水中缩合,为高产率的 C-糖苷酮提供了一种方便有效的途径。反应通常以高β'异头'立体选择性进行,因为产物组成由热力学控制决定。从机理上讲,缩合遵循典型的 Knoevenagel 方案,之后分子内的 oxa-Michael 环化通过遵循外三或内三途径确定 C-糖苷构型。对于开链 1,3-二酮,随后发生逆克莱森断裂以提供简单的糖基单酮。然后C-糖苷在反应条件下进一步缓慢脱水,得到2,5-二取代呋喃。