Intramolecular Homolytic Displacement. XXIII. Selectivity in the Induced Decomposition of Ethyl t-Butylperoxymethylpropenoate by Radicals Formed From Methyl Propanoate and Derivatives

Thermal decomposition of t-butyl peracetate in a solution of ethyl t-butylperoxymethylpropenoate in methyl propanoate led to the products of substitution of the three different hydrogens in the molecule of the methyl ester by the 2,3-epoxy-2-ethoxycarbonylpropyl group. An S(H)i reaction on the peroxide function, following the addition to the double bond, is responsible for the formation of these epoxides. Such a result is due to the low regioselectivity of the hydrogen abstraction from methyl propanoate by t-butoxyl radicals, and no improvement could be obtained by changing the relative ratios of the reactants, in converse to previous results described for similar reactions. Thus, selective creation of alkyl radicals was developed through the generation of tributylstannyl radicals as mediator radicals, by reaction of t-butoxyl radicals on tributyltin hydride or hexabutylditin; the mediator radicals abstract an iodine atom from the alkyl iodide. Application of this methodology to the three iodo derivatives of methyl propanoate permitted us to obtain selectively each of the three epoxides.