LAUSR

Abstract This work describes the oxidation of valencene, a sesquiterpene easily obtained from citrus fruits, and responsible for the fresh odor of oranges. The reactions were catalyzed by manganese porphyrins derived from 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)porphyrin (H2T3,5DMPP): [MnIII(T3,5DMPP)Cl] (MnP1) and [MnIII(Br12T3,5DMPP)Cl] (MnP2), using iodosylbenzene (PhIO), iodobenzene diacetate [PhI(OAc)2], and molecular oxygen as oxidants. The systems MnP1/O2/acetonitrile and MnP1/O2/diethyl carbonate led to higher yields of valencene oxidation products (44% and 48%, respectively) as compared with MnP2 (9% and 7%, respectively), with nootkatone being the major product. The addition of a small amount of imidazole (molar MnP1: imidazole ratio of 1:5) to the MnP1/O2/diethyl carbonate led to superior yields (64%) as compared with systems without the additive. A mechanism for the formation of the two products obtained was also proposed.