Oxidation of Unsaturated Ethers at Multiple Bonds

Vinyl ethers and peroxy acids give primarily epoxides, which can be isolated [297] or which can react further with the reaction medium [314] (equations 329 and 330). 

Stronger oxidants convert enol ethers into esters or lactones. Ethyl vinyl ether added to a suspension of pyridininm chlorodiromate (PCC) in dichloromethane at room temperature furnishes ethyl acetate in 75% yield after 1 h (equation 331) [608]. Glucals produce lactones (equation 332) [609], 

Even stronger oxidative agents such as dilute nitric acid transform 3,4-dihydro-2/f-pyran at 100 °C into glutaric acid in 70-75% yields [7755]. 

Allylic ethers are epoxidized stereoselectively to predominantly syn products with peroxytrifluoroacetic acid in dichloromethane. In tetrahy-drofuran, anti epoxidation prevails. Also, m-chloroperoxybenzoic acid in dichloromethane gives a higher proportion of anti-addition products (equation 333) [287.  

Selenium dioxide converts aryl and aralkyl allyl ethers into aldehydes and the corresponding alcohols. Allyl benzyl ether refluxed with selenium dioxide in acetic acid and dioxane for 1 h gives a 50% yield of benzyl 

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