Photorearrangements in spiro-conjoined cyclohexa-2,5-dien-1-one

The unexpected formation of cyclohexa-2,5-dien-1-one (6) spiro-conjoined with a dihydrobenzofuran framework, and the photochemical behavior of this compound in solution as well as in the solid state are described. The photoreaction of 6 in solution affords two rearranged products, one (7) accompanied by the enlargement of the oxygen heterocyclic ring and the other (8) accompanied by cyclopentadienone fragmentation. In the solid state, the former is the sole photoproduct of both solvated and desolvated crystals. The desolvated crystals were obtained as polycrystalline solids by thermal release of solvent molecules, and its structure was elucidated by ab initio determination from X-ray powder diffraction data followed by the Rietveld refinement.