We report the formal synthesis of (±)-pentalenolactone A methyl ester from simple 2-methoxyphenol. The key features of our route are as follows: a Diels-Alder reaction of masked o-benzoquinone to assemble the functionalized bicyclo[2.2.2]octenone, a continuous-flow oxa-di-π-methane rearrangement for building the diquinane core (AB ring), and an oxidative cleavage/oxidation sequence for annulation of the δ-lactone (C ring).