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.

New silver‐catalyzed tunable dimerization and trimerization reactions of β‐alkynyl ketones have been established, enabling multiple C−C bond‐forming events to selectively access skeletally diverse spiroisochromenes with generally good yields. The silver‐enabled bicycloaddition of β‐alkynyl ketones with water offered hydroxylated spiroisochromenes. Without water, spiroisochromenes with a methylene moiety were obtained through catalytic 6‐endo‐dig oxo‐cyclization/[4+2] cycloaddition cascades by using pyridine as additive whereas employment of 1,1′‐binaphthyl‐2,2′‐diyl hydrogen phosphate (BiNPO4H) as a Brønsted acid catalyst rendered the unprecedented dispiro trimerization products through double C(sp3)–H functionalization.magnified image

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.

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