Bicyclo[1.1.1]pentanone. Synthesis, Thermal Chemistry, and Photochemistry

Bicycle[1.1.1]pentanone (1) has been prepared in two steps, the key reaction being the ozonolysis of 2-phenylbicyclo[1.1.1]pentan-2-ol (6). On heating, 1 undergoes cycloreversion to allylketene (13). The activation parameters and solvent effects for this process suggest that the reaction is concerted and that the transition state is relatively nonpolar. The predominant photochemical pathway for 1 is decarbonylation to bicyclobutane (16). Cycloreversion to 13 is a minor reaction mode. Both the thermal and photochemical results are rationalized by considering the high strain energy and novel geometrical features of 1, and, in the latter case, the unusually high energy of its ¹(nΠ^*) state.