Synthesis and Ultraviolet Absorption Characteristics of Chiral 3-arylidenenopinones from β-pinene

A new series of (1R, 5R)-(-)-3-arylidenenopinones was synthesized from (1S, 5S)-(-)-beta-pinene which was a natural chemical from pine tree, and their ultraviolet absorption characteristics were investigated. (1R, 5S)-(+)-nopinone was obtained from (1S, 5S)-(-)-beta-pinene by selective oxidation, and then it was reacted with benzaldehyde, p-hydroxybenzaldehyde, vanillin, o-vanillin, p-chlorobenzaldehyde, and p-methylaldehyde in the presence of alkali catalysts to get (1R, 5R)-(-)-3-arylidenenopinones including (1R, 5R)-(-)-3-benzylidenenopinone (1), (1R, 5R)-(-)-3-(4'-hydroxybenzylidene) nopinone (2), (1R, 5R)-(-)-3-(4'-hydroxy-3'-methoxybenzylidene) nopinone (3), (1R, 5R)-(-)-3-(2'-hydroxy-3'-methoxybenzylidene) nopinone (4), (1R, 5R)-(-)-3-(4'-chlorolbenzylidene) nopinone (5) (1R, 5R)-(-)-3-(4'-methylbenzylidene) nopinone (6), and (1R, 5R)-(-)-3-(furan-2'-ylmethylene) nopinone (7). The structures of (1R, 5R)-(-)-3-arylidenenopinones were determined by FT-IR, H-1 NMR, C-13 NMR and GC-MS techniques. Their ultraviolet absorption characteristics and light stability was further examined. The results showed that compounds 1, 2, 5, 6 and 7 could be used as B-type UV absorbents, and compounds 3 and 4 had both functions as UV-A and UV-B types absorbents because of their wide range of UV absorption at 200-390 nm and 280-290 nm respectively. The light stability sequence of these compounds was (6)approximate to(7)>(3)>(5)>(2)>(1)>(4).