Synergistic Pd/Ag-Catalyzed Domino Reaction: Access to Tetrahydropyrano[4,3-c]pyran and Hexahydrofuro[2,3-b]pyran.

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We report the Pd-catalyzed and Ag-mediated temperature-dependent divergent synthesis of tetrahydropyrano[4,3-c]pyran and hexahydrofuro[2,3-b]pyran derivatives from a single substrate, alkynols. The reaction involves homocoupling of alkynols to form two C-O bonds and one C-C bond, resulting in tetrahydropyrano[4,3-c]pyran cores at a high temperature (110 °C). Exposing tetrahydropyrano[4,3-c]pyrans to a 200 W tungsten filament bulb yields tetrahydrofuro[2,3-b]pyrans. At lower temperatures (30-60 °C), alkynols produce hexahydrofuro[2,3-b]pyrans. The density functional theory study explains temperature-dependent selectivity.