Alkyl-substituted epoxides, cleavage

In Pd(0)-catalyzed isomerization reaction of epoxides, alkyl-substituted epoxides afford methyl ketones (path a, Scheme 11), whereas aryl-substituted epoxides give aldehydes or ketones via cleavage of the benzylic C-O bond (path b) [94]. 

Among alkyl-substituted ethylene oxides known to umletrn cleavage on treatment with sodium sulfite are propylene oxide, isobutylene oxide, 1,2-epoxybutane, 1,2-epoxyoctane, and 2,3-cpow-butane.1 75 These reactions with sodium sulfite constitute the bani-, ffrail analytical method developed by Swan1875 for the estimation <[Pg.179]

Hydration of aryl-substituted epoxides. Treatment of aryl-substituted oxiranes with copper(II) sulfate and pyridine in an aqueous phosphate buffer (pH 7) affords cis-diols by reaction of water at the benzylic position. Less than 15% of trans cleavage products obtain. In the absence of pyridine, the oxides are rapidly destroyed. Triethylamine cannot be substituted for pyridine. cis-Chlorohydrins are obtained when aryl-substituted oxides are treated with copper(II) sulfate, pyridine, and kiCl in THF, When methanol is used as solvent, the corresponding cis-glycol monomethyl ether is obtained. In all cases substitution occurs at the benzylic position. Alkyl oxiranes do not react under these conditions. ... 

Ethers are generally unreactive except with strong acids such as HI and HBr, which leads to cleavage of the ether to an alcohol and an alkyl halide. Epoxides are particularly reactive with nucleophiles, which open the three-membered ring at the less substituted carbon. Epoxides also react with an acid catalyst and weak nucleophiles such as water or alcohols, as well as with cyanide, azide, etc. 

HX Will convert dialkyl ethers into alkyl halides via cleavage of the C-O bonds. Will also react with an epoxide, thereby opening the ring, and installing a halogen at the more substituted position. 

The organocopper reagents prepared in this way cleave epoxides in high yield with substitution of the alkyl group at the less hindered site. This cleavage has been used to effect intramolecular cyclization (second example). 

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