Readily available 1,2-amino alcohols provide the framework for a new generation of chiral carboxylicacid catalysts that rival the acidity of the widely used chiral phosphoric acid catalyst (S)-TRIP. Covalently linked thiourea sites stabilize the carboxylate conjugate bases of these catalysts via anion-binding, an interaction that is largely responsible for the low pKa values. The utility of the new
A Facile Synthesis of <b><i>trans</i></b>-Fused Pyrano[3,2-<i>c</i>]benzopyrans Catalyzed by Scandium Triflate
作者:Jhillu Yadav、Basi Reddy、M. Aruna、M. Thomas
DOI:10.1055/s-2002-19810
日期:——
Scandium triflate has been utilized as an efficient Lewis acid for the intramolecular cycloaddition of o-quinonemethides (generated in situ from salicylaldehydes and unsaturated alcohols) to afford the corresponding trans-fused pyranobenzopyrans in high yields with high selectivity.
Stereoselective Synthesis of Pyrano[3,2-<i>c</i>]benzopyrans via Intramolecular Cycloaddition of <i>o</i>-Quinonemethides Generated from Salicylaldehydes and Unsaturated Alcohols under Very Mild Conditions
Intramolecular [4 + 2] cycloaddition reaction of 6-(4-alkenyloxymethylene)-2,4-cyclohexadien-1-ones generated from the reaction between substituted salicylaldehydes and unsaturated alcohols under mild conditions was investigated. In general, the reaction furnished tricyclic compounds containing the pyranobenzopyran skeleton with trans-fused B/C ring in very good yields (Tables 1 and 2). Furthermore, geometry of the olefinic bond of the starting material is retained during the reaction.
[4+2] Cycloaddition ofortho-Quinone Methides Promoted by Ionic Liquids: an Efficient and Mild Protocol for the Synthesis of Tetrahydropyranobenzopyrans
作者:J. S. Yadav、B. V. Subba Reddy、K. Sadashiv、B. Padmavani
DOI:10.1002/adsc.200303198
日期:2004.5
The stereoselective synthesis of trans-annelated pyrano[3,2-c]benzopyrans has been achieved by intramolecular [4+2] cycloaddition of o-benzoquinone methides that are generated in situ from o-hydroxybenzaldehydes and unsaturated alcohols using an air- and moisture-stable ionicliquid, i.e., 1-butyl-3-methylimidazolium tetrafluoroborate [bmim]BF4 under mild and neutral conditions.
通过分子内[4 + 2]邻苯甲醌甲基化物的环内[4 + 2]环加成反应,可以通过空气和水分从邻羟基苯甲醛和不饱和醇中原位生成反式吡喃并[3,2- c ]苯并吡喃的立体选择性合成。稳定的离子液体,即在中性和中性条件下的四氟硼酸1-丁基-3-甲基咪唑鎓[bmim] BF 4。