The "photo-Friedel-crafts acylation" of 1,4-naphthoquinones

The photochemical reaction between 1,4-naphthoquinone (3) and several aliphatic and aromatic aldehydes 5a-f resulted in the formation of acylated naphthohydroquinones 6a-f in moderate to good yields of 42-79%. When benzaldehyde was used, the dibenzoylated product 7 was also isolated, in 14% yield. The regioselectivity was studied with the unsymmetrical substituted naphthoquinone 4 and butyraldehyde 5b and benzaldehyde 5f. With 5f, the corresponding diaroylated compound 12 was again isolated as a minor product. Oxidation of selected photoproducts afforded the corresponding acylated naphthoquinones 8a, 8b, 8f, and 13 in moderate to excellent yields of 53-94%.