5-Alkyl-substituted epoxides, rearrangement

In conclusion, the ability to abstract the -proton is correlated to its degree of substitution. However, substituents other than simple aUcyl groups may modify this facility of proton removal and influence the course of the -elimination. As anticipated, the presence on the adjacent carbon of the epoxide of an ally lie or benzylic group results in a dramatic enhancement of the -elimination rate and modifies its regioselectivity . As shown in Scheme 19, the rearrangement of the phenyl-substituted epoxide 34 is complete within a few minutes, whereas several hours are required in the case of the corresponding alkyl-substituted epoxide 35. 

The reaction involving 0-hydroxyalkyl selenones is by far the less attractive route to qroxides among those cited above due to the difficulties usually encountered in the oxidation step and the easy rearrangement of the p-hydroxyalkyl selenones to carixmyl compounds (Scheme 184, b and c). This method is, however, particulariy useful for the synthesis of oxaspnopentanes (especially for those bearing a fully alkyl-substituted epoxide ring) ftom l-seleno-l-(r-hydroxyalkyl)cyclopropanes (Scheme 163, e Scheme 18S), which caruiot be obtained under other conditions. ... 

Oxidation of Other Arenes. Aromatic compounds with longer alkyl side chains can be converted to ketones or carboxylic acids. All the previously discussed reagents except Cr02Cl2 usually afford the selective formation of ketones from alkyl-substituted arenes. Oxidation with Cr02Cl2 usually gives a mixture of products. These include compounds oxidized in the P position presumably formed via an alkene intermediate or as a result of the rearrangement of an intermediate epoxide.110,705... 

Gallium(III) triflate catalysed the rearrangement of 2-substituted vinyl epoxides into /3,y-unsaturated carbonyl compounds with high regio- and chemo-selectivity with low catalyst loading. Alkyl-substituted trimethylsilylvinyl epoxides gave /i,y-unsaluralcd ketones, but aryl-substituted vinyl epoxides gave the aldehydes.80... 

The rearrangement of tri- and tetra-substituted epoxides by this reagent involves anri-migration of the alkyl groups.3... 

The catalytic acid rearrangement of 9a-hydroxyparthenolide (Scheme 68) and 5-alkyl-substituted diphenylhomobenzoquinone epoxides has been reported (Scheme 69). ... 

Alkyl- and aryl-hydrazones of aldehydes and ketones readily peroxidise in solution and rearrange to azo hydroperoxides [1], some of which are explosively unstable [2], Dry samples of the p-bromo- and p-fluoro-hydroperoxybenzylazobenzenes, prepared by oxygenation of benzene solutions of the phenylhydrazones, exploded while on filter paper in the dark, initiated by vibration of the table or tapping the paper. Samples were later stored moist with benzene at —60°C to prevent explosion [3], A series of a-phenylazo hydroperoxides derived from the phenyl-or p-bromophcnyl-hydrazones of acetone, acetophenone or cyclohexanone, and useful for epoxidation of alkenes, are all explosive [4], The stability of several substituted phenylazo hydroperoxides was found to be strongly controlled by novel substituent effects [5],... 

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