Synthesis of Spiroketals by Synergistic Gold and Scandium Catalysis.

An ultrafast synthesis of spiroketals by synergistic gold(I) and Sc(III) catalysis has been reported. Diverse 5,6-benzannulated spiroketals were rapidly constructed by the diastereoselective [4 + 2] cycloaddition between gold-generated enol ether and Sc(III)-catalyzed o-quinone methide intermediates. Ultrafast reaction rate, ambient reaction temperature, general scope, high yields, excellent diastereoselectivity, and good scalability are attractive features of this method.