We report a dearomative (5+2) cycloaddition/oxa-Michael addition cascade strategy that enables concise construction of functionalized bridged [4.3.1] bicyclic frameworks. This base-mediated, one-pot process reveals an unconventional reactivity mode of alpha-arylidene pyrazolones, wherein they function as C2 synthons in dearomative addition to oxidopyrylium intermediates derived from readily accessible acylated pyranones, affording oxygen-bridged [4.3.1] bicycles bearing four stereocenters with excellent diastereocontrol. DFT studies firmly establish the operative reaction pathway and indicate (3+3) spiroannulation as a crucial competing process consistent with the experimental findings.

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