Metal-Free Epoxidation of Alkenes with Molecular Oxygen and Benzaldehyde under Visible Light Irradiation

Abstract

A new convenient metal-free oxidation protocol of a wide variety of alkenes with molecular oxygen and benzaldehyde under visible light irradiation of fluorescent lamp afforded their corresponding epoxides in 49-99% yields

Key words

aerobic - epoxidation - visible light - benzaldehyde

References and Notes

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6

Exposure of benzaldehyde to the molecular oxygen under visible light irradiation in the presence of trans-stilbene (1) result in the no reaction, probably because trans-stilbene (1) inhibits photooxidation of benzaldehyde. On the other hand, 11% of trans-5-decene oxide was produced when using trans-5-decene instead of 1.

7

Typical Procedure of the Epoxidation
A dry MeCN solution (1 mL) of the benzaldehyde (63.7 mg, 0.6 mmol) in a 30 mL round-bottom flask equipped with
an O₂ balloon was stirred and irradiated with four 22 W fluorescent lamps, which were set up at a distance of 65 mm, for 3 h. The temperature of the final stage of this reaction was about 50 ˚C. Then, trans-stilbene (1, 54.1 mg, 0.3 mmol) was added to the reaction mixture and stirred without irradiation for 10 h at r.t. The reaction mixture was concentrated under reduced pressure. The residue was purified by preparative TLC to afford the pure product 2 (52.4 mg, 89%).

8

Yield of perbenzoic acid was determined by integration of ^¹H NMR with internal standard (1,1,2,2,-tetrachloroethane).