Photochemical Reaction of Perillaldehyde under Various Conditions.

(-)-PeriIlaldehyde (1) was photoirradiated by a 400 W high-pressure mercury lamp under various conditions. In MeOH, 1 was degraded to give two new MeOH adducts (2 and 3) and a new methyl ether (4) under an N2 stream, while 1 was converted to a dimethyl acetal (5) and oxidation product (6) in addition to 2 and 3 under an 02 stream. In EtOAc, 1 disappeared to afford two new dimers (7 and 8) under an N2 stream, while 1 was changed to two oxygenated products (9 and 10) including a new compound under an O2 stream. In the presence of rose bengal (RB), 1 was converted to 5 by visible light in MeOH under an N2 stream. Photosensitization of RB was observed under an O2 stream, and two new oxygenated products (11 and 12) were formed. Perillaldehyde was relatively stable in n-hexane under an N2 stream or in the presence of RB under an O2 stream.