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.