Domino Reactions of 1,3‐Bis‐Silyl Enol Ethers with Benzopyrylium Triflates: Efficient Synthesis of Fluorescent 6 H ‐Benzo[ c ]chromen‐6‐ones, Dibenzo[ c,d ]chromen‐6‐ones, and 2,3‐Dihydro‐1 H ‐4,6‐dioxachrysen‐5‐ones

The condensation of 1,3‐bis‐silyl enol ethers with benzopyrylium triflates, generated in situ by the reaction of chromones with Me 3 SiOTf, afforded functionalized 2,3‐dihydrobenzopyrans; treatment of the latter with NEt 3 or BBr 3 resulted in a domino retro‐Michael–aldol–lactonization reaction and the formation of a variety of 7‐hydroxy‐6 H ‐benzo[ c ]chromen‐6‐ones. The hydroxy group was functionalized by using Suzuki cross‐coupling reactions. The methodology reported was applied to the synthesis of the natural product autumnariol and a new fluorescence dye, which exhibits promising optical properties. 2,3‐Dihydro‐1 H ‐4,6‐dioxachrysen‐5‐ones were prepared by condensation of chromones with 1,3‐bis‐silyl enol ethers containing a remote chloride group, domino retro‐Michael–aldol–lactonization, and an intramolecular Williamson reaction.