J. Mihara et al., Photo-controlled Lewis acidity: Chiral (ON)Ru-salen catalyzed hetero Diels-Alder reaction and kinetic resolution of racemic epoxides, SYNLETT, (7), 1999, pp. 1160-1162
(ON+)(Salen)ruthenium(II) complex 1 serves as a chiral Lewis acid catalyst
for asymmetric hetero Diels-Alder reaction and for kinetic resolution of ra
cemic epoxides when the reactions were carried out under sunlight coming th
rough windows or incandescent light.