Lewis Acid-Catalyzed 1,4-Addition and Annulation of 4-Hydroxy-coumarins with <i>o</i>-Hydroxyphenyl Propargyl Amines: Entry to Regio-Selective Synthesis of Furano[3,2-<i>c</i>]coumarins and Pyrano[3,2-<i>c</i>]coumarins
Ganesh Shivayogappa Sorabad, Ding‐Yah Yang
Abstract
A facile and regioselective Lewis acid-catalyzed cascade annulation of o -hydroxyphenyl propargyl amines with 4-hydroxycoumarin to afford furano[3,2- c ]coumarin and pyrano[3,2- c ]coumarin derivatives is reported. The reaction presumably proceeds by the conjugate addition of 4-hydroxycoumarin to the in situ-generated alkynyl o -quinone methide and is followed by intramolecular 5- exo-dig and 6- endo-dig annulation to form furano[3,2- c ]coumarins and pyrano[3,2- c ]coumarins, respectively. The prepared o -hydroxyl substituted pyrano[3,2- c ]coumarins could be readily transformed into the corresponding coumarin-derived dioxabicycles by acid-mediated cyclization.
Topics & Concepts
AnnulationChemistryPropargylCoumarinRegioselectivityLewis acids and basesIntramolecular forceCatalysis4-HydroxycoumarinStereochemistryMedicinal chemistryOrganic chemistrySynthesis of Indole DerivativesSynthesis of Organic CompoundsSulfur-Based Synthesis Techniques