Photochemistry of acetone in the presence of exocyclic olefins: an unexpected competition between the photo-Conia and Paternò–Büchi reactions

When irradiated in the presence of several exocyclic olefins, acetone undergoes homoalkylation with the olefins to form a series of 4-cycloalkylbutan-2-ones (with quantum yields of 0.14 ± 0.01) rather than exhibiting the expected Paternò–Büchi reaction; in contrast, the photolysis of perdeuteriated acetone gave both types of products.