Epoxidations with chromic oxide

Hickinbottom and co-workers have reported several instance in which olefins were converted into epoxides with chromic oxide in ocetir anhydride. 76 42 776-718 Rarely were the desired epoxides the only products formed, however. Two or more carbonyl compounds were usually produced as well. A few illustrations will suffice to demonstrate the subtleties of the structure-reactivity relationship for this reaction. 

Oxidations with chromic oxide encompass hydroxylation of methylene [544] and methine [544, 545, 546] groups conversion of methyl groups into formyl groups [539, 547, 548, 549] or carboxylic groups [550, 55i] and of methylene groups into carbonyls [275, 552, 553, 554, 555] oxidation of aromatic hydrocarbons [556, 557, 555] and phenols [559] to quinones, of primary halides to aldehydes [540], and of secondary halides to ketones [560, 561] epoxidation of alkenes [562, 563,564, and oxidation of alkenes to ketones [565, 566] and to carboxylic acids [567, 565, 569]. 

When heated in the presence of a carboxyHc acid, cinnamyl alcohol is converted to the corresponding ester. Oxidation to cinnamaldehyde is readily accompHshed under Oppenauer conditions with furfural as a hydrogen acceptor in the presence of aluminum isopropoxide (44). Cinnamic acid is produced directly with strong oxidants such as chromic acid and nickel peroxide. The use of t-butyl hydroperoxide with vanadium pentoxide catalysis offers a selective method for epoxidation of the olefinic double bond of cinnamyl alcohol (45). 

Other tetrasnhstituted olefins (Eq. 115) have recently boon reported18 4-1844 to yield the corresponding epoxides on oxidation with chromic noid in glacial acetic add, Mosher and co-workers also noted in addition the formation of significant proportions of cyclic carbonate when all traces of winter were excluded from tfio reaction medium by addition of acetic anhydride.1944... 

The acid-catalysed cleavage of the 9j8,lljS-epoxide (188) by acetonitrile in the presence of an acid afforded the corresponding 9a-acetamido-lljS-hydroxy-derivative (189). On oxidation with chromic acid in the presence of acetic acid, the isoxazoline (190) was formed. 

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