Synthesis of Fulvene Vinyl Ethers by Gold Catalysis.

Gold‐catalyzed cyclization of 1,5‐diynes with ketones as reagents and solvent provides diversely substituted vinyl ethers under mild conditions. The regioselectivity of such gold‐catalyzed cyclizations is usually controlled by the scaffold of the diyne. Herein, we report the first solvent‐controlled switching of regioselectivity from a 6‐endo‐dig‐ to 5‐endo‐dig‐cyclization in these transformations, providing fulvene derivatives. With respect to the functional‐group tolerance, aryl fluorides, chlorides, bromides, and ethers are tolerated. Furthermore, the mechanism and selectivity are put to scrutiny by experimental studies and a thermodynamic analysis of the product. Additionally, 6‐(vinyloxy)fulvenes are a hitherto unknown class of compounds. Their reactivity is briefly evaluated, to give insights into their potential applications. [ABSTRACT FROM AUTHOR]