20534-58-1

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The reaction of methyl(trifluoromethyl)dioxirane (1b), a novel dioxirane species, with two open-chain, four cyclic, and five polycyclic saturated hydrocarbons and two aralkyl hydrocarbons in CH2Cl2/1,1,1-trifluoropropanone has been studied; under mild conditions (-22 to 0 deg C), it gives alcohols and/or ketones (deriving from further oxidation of secondary alcohols) in high yields and within very short reaction times.Primary C-H bonds are not appreciably oxidized and high regioselectivities were determined for attack at tertiary over secondary C-H bonds, with theexception of norbornane, which showed opposite regioselectivity.The reaction is also highly stereoselective, since hydroxylations of cis- and trans-decalin and of cis- and trans-1,2-dimethylcyclohexane were found to be in each case stereospecific with retention.From kinetic data, Ea = 14.3 kcal mol-1 and log A = 9.9 were estimated for cyclohexane oxidation.Relative rates change in the order cyclohexane (0.78) octane (9.2) adamantane (146); cis-1,2-dimethylcyclohexane was observed to be 7-fold more reactive than its trans isomer, demonstrating remarkable discrimination for equatorial vs axial C-H attack (also noticed in the case of cis- and trans-decalin).The relative rate of oxidation of cumene vs ethylbenzene was found to be ca. 3.1 (after statistical correction), i.e., in sharp excess over values usually recorded in classical radical H-atom abstraction from benzylic position.Rate constants determined for the reactions of cumene and of ethylbenzene show the title dioxirane (1b) is more reactive than dimethyldioxirane (1a) by factors of ca. 600 and over 700, respectively.The whole of theobservations is better accommodated by an "oxenoid" mechanism, involving concerted O-atom insertion by dioxirane into C-H bonds of hydrocarbons.

The reaction of ozone with norbornane, adamantane and bicyclooctane has been studied, including kinetics and product studies as well as the determination of activation paprameters for the ozonation of norbornane.This work was carried out to distinguish between hydride abstraction and a concerted insertion mechanism for the ozonation of C-H bonds.Kinetically, norbornane behaves like a secondary hydrocarbon and lacks the rate acceleration expected if a carbocation intermediate were involved in a hydride abstraction mechanism.We interpret this and other results as supporting a 1,3-dipolar insertion mechanism for the reaction of ozone with C-H bonds.

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The migration aptitudes of cyclic and polycyclic bridgehead groups in the Criegee Rearrangement support ?-neighbouring group participation by pentacoordinated bonding and vertical charge stabilisation in the migrating group and therefore favour transition state 2b and not 2a.

Peracids RCO3H yield free radicals R. which react either with the peracid or with solvent giving the alcohol ROH and the hydrocarbon RH.The nucleophilic character of the free radicals was modified either by substitution of the carbon bearing the odd electron by inductive groups or by changing the free radical hybridation by the means of blocked structures such as cyclic or bicyclic free radicals.For each R., the measurement of the ratio ROH/RH establishes a reactivity scale for R. with the peracid O-O bond.This reactivity does not depend on free radical stability but depends strongly on nucleophilic character.A primary free radical is less reactive than a secondary one, and is much less reactive than a tertiary one.A bridgehead free radical as the bicycloheptyle-1 does not react with the peracid.These results are interpreted to indicate a transition state with charge transfer (polar effect), the peracid being electrophilic and the free radical nucleophilic; PMO theory is discussed.