Ring Size Effect on the Photoreaction of [n.3.2]Propellanones Involving a Cyclobutanone Ring

In the photoreactions in methanol of [n.3.2]propellanones 1-4 and [n, 3.2]propellanediones 5-8 involving a cyclobutanone ring, cycloelimination products show increasing predominance over ring-expansion products with increasing third-ring size. In addition, in the case of 5-8, the yield of the syn-form acetals 16a-19a was slightly more than the yield of the anti-form acetals 16b-19b, and the syn/anti ratio increases by degrees as the third ring changes from a five- to an eight-membered ring. These ring size effects are discussed.