Directing Group Assisted Nucleophilic Substitution of Propargylic Alcohols via o-Quinone Methide Intermediates: Bronsted Acid Catalyzed, Highly Enantio- and Diastereoselective Synthesis of 7-Alkynyl-12a-acetamido-Substituted Benzoxanthenes

BINOL-based, chiral phosphoric acids catalyze the substitution of 1-(o-hydroxyphenyl)propargylic alcohols with enamides to furnish 7-alkynyl-12a-acetamido-substituted benzo[c]xanthenes and related heterocycles in a one-pot operation with excellent diastereo- and enantioselectivity. Ambient reaction temperature, operationally simple reaction conditions, low catalyst loading, high yields, and excellent stereocontrol are attractive features of this process and make it a highly practical and versatile transformation.