Perepoxide intermediates in the conversion of some β-halohydroperoxides to allylic hydroperoxides by base

Abstract

. Migration of the hydroperoxy group occurs during the reaction between base and several 0-halohydroperoxides to give allylic hydroperoxides. An 86: 14 ratio of 3-hydroperoxy-2-(4-methoxypheny1)-3-methyl-I-butene-3-hydroperoxy-3-(4-methoxyphenyl)-2-methyl-I-butene was formed in 90% yield from 2-bromo-3-hydroperoxy-3-(4-methoxyphenyl)-2-methylbutane. From I-chloro-, I-bromo-, and I -iodo-I-(I-hydroperoxy-I-methylethy1)cyclohexane there were obtained I-(I-hydroperoxy-1-methylethyl)cyclohexene and I-hydroperoxy-I-(2-propeny1)-cyclohexane in ratios of 93:7, 94:6, and 94:6, respectively, in 98-100% yield. Isopropylidenecyclohexane was converted with singlet oxygen t o these allylic hydroperoxides in a 10:90 ratio. Only the latter allylic hydroperoxide was formed in the reaction between the alkene and triphenyl phosphite ozonide at -70°C. The p-nitrobenzoate esters of I-hydroperoxy(1-chloro-, I-bromo-, and I-iodo-I-methylethyl)cyclopentane were converted quantitatively to I-(I-hydroperoxy-I-methylethyl)cyclopentene and I-hydroperoxy-I-(2-propeny1)-cyclopentane in 77:23, 73:27, and 70:30 ratios, respectively. Oxidation of isopropylidenecyclopentane with triphenyl phosphite ozonide at -70°C and singlet oxygen produced the allylic hydroperoxides in 62:38 and 58:42 ratios, respectively. The reactions of the p-halohydroperoxides proceed exclusively via perepoxide intermediates. T h e reactions between the alkenes and singlet oxygen or triphenyl phosphite ozonide do not involve perepoxide intermediates.

The mechanism of the ene reaction of singlet oxygen with olefins

“…Jefford further suggested that the methoxy results are simply a special case of this. This mechanism does not, however, explain the lack of cyclopropyl H abstraction products found by Conia56 when the methoxy groups in (24) are replaced with methyl. The effect pointed out by Jefford may be important in alkyl olefins, but it is not sufficient to explain the polar-group directing effect.…”

Liquid-phase regioselective 1,4-hydrogenation of benzylidene ketones on rhodium-aluminum phosphate catalysts

“…The rate data were fitted to the Pavelich-Taft equation in an attempt to correlate relative reactivities with enthalpic ( ) and steric (Eg) constants. A reasonably good fit was obtained for the equation log(&/&o) = Ph°H + <>xEg (2) where k0 is the reaction rate for X = Me, k is the rate for the X group, and Eg are the substituent parameters which are characteristic for the enthalpic and steric effects, respectively, and pH and the corresponding reaction constants.…”

Triphenyl Phosphite Ozonide

“…Singlet oxygen product ratios were also obtained 15, 16 by two groups when the substrate is 1,2-dimethylcyclohexene. Kopecky et al 17 showed that reaction of isopropylidenecyclohexane with (1) gives two hydroperoxide products in a ratio which is closer to that given in a reaction believed to involve singlet oxygen and quite different from that obtained in a base-catalyzed displacement reaction of the appropriate β-halohydroperoxide.…”