J

Irradiation of trans-methyl cinnamate in dry CH3CN solvent under argon in a Pyrex reactor with a high-pressure mercury lamp resulted in the formation of a photostationary state consisting of 49% cis- and 51% trans-isomer. In the presence of Sc(OTf)3 (molar ratio of Sc(OTf)3 / trans-methyl cinnamate = 2.0), a photostationary state mixture of 88% cis- and 12% trans-isomer was obtained under the same irradiation condition. After this photoisomerization, Sc(OTf)3 could be recovered quantitatively and reused with no loss of activity. In the use of other rare-earth metal triflates, Yb(OTf)3 and Y(OTf)3, the conversion of the photoisomerization of trans-methyl cinnamate to cis-isomer increased slightly. The irradiation of trans-ethyl cinnamate and trans-benzyl cinnamate in the presence of Sc(OTf)3 (molar ratio of Sc(OTf)3 / trans-cinnamate = 2.0) afforded cis-ethyl cinnamate (88%) and cis-benzyl cinnamate (83%), respectively. Even in commercial CH3CN solvent without any treatment under the atmosphere, the irradiation of these trans-cinnamates in the presence of Sc(OTf)3 resulted in the optimum conversion to the corresponding cis-isomers.