Asymmetric Cycloaddition of ortho-Hydroxyphenyl-Substituted para-Quinone Methides and Enamides Catalyzed by Chiral Phosphoric Acid.

A BINOL-based chiral phosphoric acid was employed as an efficient catalyst in enantioselective cycloaddition of ortho-hydroxyphenyl-substituted para-quinone methides and enamides, which gave rise to acetamido-substituted tetrahydroxanthenes with three adjacent stereogenic centers in high yields (up to 99%) and excellent stereoselectivities (up to >99:1 diastereomeric ratio and up to 98% ee).