In two very proximate syn-periplanar (“face-to-face”) systems (shortest π,π-distances of ca. 3.0 Å, X-ray), photoequilibration (ratio ca. 2:1) with the cyclobutane-photo[6+6]cycloadducts has been installed by 254 nm irradiation. The “dimers” are thermally persistent enough as to allow pagodane formation through the cycloaddition of dienophiles.