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-potmethod for silver-catalyzedtandemcycloisomerization/[5 + 2] cycloaddition reactions between readilyaccessible cyclopropyl-tethered allenyl ketones and benzopyranone-derivedoxidopyrylium ylides. The reactions proceed via acyclobutene-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 bibridgedbenzocycloheptanones bearing a strained cyclobutane ring and an O-bridged ring.