Silver-Catalyzed Tandem Cycloisomerization/[5 + 2] Cycloaddition of 3‑Cyclopropylideneprop-2-en-1-ones with Oxidopyrylium Ylides to Form Bibridged Benzocycloheptanones

Herein, we report a mild, one-pot method for silver-catalyzed tandem cycloisomerization/[5 + 2] cycloaddition reactions between readily accessible cyclopropyl-tethered allenyl ketones and benzopyranone-derived oxidopyrylium ylides. The reactions proceed via a cyclobutene-fused furan intermediate generated in situ by a cycloisomerization/1,2-carbene transfer/ring-expansion cascade. This method, which features an unprecedented formal [5 + 2] cycloaddition, delivers good to excellent yields of structurally complex bibridged benzocycloheptanones bearing a strained cyclobutane ring and an O-bridged ring.