AbstractThe readily available benzodihydropentalene6and dimethyl acetylene‐dicarboxylate react to give norbornadiene diester8, with a three‐carbon bridge from C1to C2. Inrradiation of8gives the corresponding C1‐C2bridged quadricyclane diester9, a new ring system. Diester9is quite stable, reverting to8with at1/2of 30 min at 170°C. The corresponding diacid11, also prepared, reverts to its norbornadiene precursor at a considerably lower temperature, possibly as a consequence of acid cat