Thermal rearrangement of spirans (14) and (31) yields the xanthones (16,34) and diphenylrnethane (15, 32), respectively. The structure for xanthone (16), isolated from thermolysis, has been established by reduction to xanthene (20) followed by reoxidation to give xanthone (16). Alternatively, methylation of the diphenylmethane (15) followed by heating with selenium dioxide also yields xant...