Irradiation of 4,4-dimethy 1-2-cyclohexenone in the presence of tetramethylethylene gives trans-5,5,7,7,8,8- hexamethylbicyclo[4.2.0]octan-2-one and an oxetane as major products. In addition, two novel secondary photoproducts are isolated and characterized. © 1969, American Chemical Society. All rights reserved.