amine-catalyzed cascade reactions with various methyl ketones to give a direct access to C-glycosides by an operationally simple protocol. As the reaction mechanism, an aldolcondensation followed by an intramolecular conjugate addition is assumed. Unprotected carbohydrates were reacted in amine-catalyzed cascade reactions with various methyl ketones to give a direct access to C-glycosides by an operationally
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
A versatile and convenient route to ketone C-pyranosides and ketone C-furanosides from unprotected sugars
作者:Junfeng Wang、Qin Li、Zemei Ge、Runtao Li
DOI:10.1016/j.tet.2011.11.029
日期:2012.1
Both ketone C-pyranosides (in up to 97% yields) and C-furanosides (in 83–97% yields) could be prepared, respectively, from the condensations of pentane-2,4-dione and various unprotected sugars in sodium carbonate aqueous media by adjusting the reaction conditions.