Asymmetric Epoxidation with a Photoactivated [Ru(salen)] Complex

(Nitrosyl)(salen)ruthenium(II) complex 1 was found to serve as an efficient catalyst for the epoxidation of conjugated olefins under photoirradiation, with 2,6‐dichloropyridine N‐oxide (2) or tetramethylpyrazine N,N′‐dioxide as a stoichiometric oxidant. High enantioselectivity was achieved irrespective of the substitution pattern of olefins. The choice of solvent depends on stability of the resulting epoxides: high enantioselectivity is generally observed in the reaction with ethereal solvents, but use of benzene is recommended when the resulting epoxides are acid‐sensitive. The first example of an asymmetric catalyst activated by photoirradiation is reported. A mixture of second‐generation [RuCl(salen)(NO)] catalyst (1), 2,6‐dichloropyridine N‐oxide or tetramethylpyrazine N,N′‐dioxide, and conjugated olefin was irradiated with visible light to produce optically active epoxide with high enantioselectivity and geometrical retention, irrespective of the substitution pattern of the olefin.