Synergistic silver/scandium catalysis for divergent synthesis of skeletally diverse chromene derivatives.

The combination of AgTFA and Sc(OTf) enables the bimetallic synergistic catalysis of β-alkynyl ketones and o-hydroxybenzyl alcohols, allowing divergent synthesis of three classes of skeletally diverse chromene derivatives with generally good yields and high diastereoselectivity through dehydroxylated bi- and tri-cyclization cascades. The selectivity of these cycloadditions was controlled by adjusting the catalyst loading and reaction temperatures. The mechanisms for forming these compounds were proposed.

Ag/Brønsted Acid Co-Catalyzed Spiroketalization of β-Alkynyl Ketones toward Spiro[chromane-2,1'-isochromene] Derivatives.

A new Ag/Brønsted acid co-catalyzed spiroketalization of β-alkynyl ketones with para-quinone methides (p-QMs) has been established, enabling multiple C-C and C-O bond-forming events to access densely functionalized spiro[chromane-2,1'-isochromene] derivatives with generally excellent diastereoselectivity and good yields. A reasonable mechanism for forming these 6,6-dibenzannulated spiroketals involving 6-endo-dig oxo-cyclization and 1,6-addition-cyclization cascades is proposed.