Peroxy esters free radicals from

Mechanistic probes based on typical cleavage, cyclization and chain-propagating reactions of free radicals were used as evidence for SET reactivity from RMgHal to peroxy esters [51] and acetylenic or vinylic sulfones [64,65]. 

Example 5.5. Oxidation of paraffins to secondary alcohols. Alcohols can be produced by oxidation of paraffins with air or oxygen at moderate temperatures (typically 120 to 180° C) in the presence of boric-acid esters or boroxines [16-18], These intercept the alkyl peroxide, the first oxidation product, preventing it from generating free radicals that would cause further degradation including scission of carbon-carbon bonds and produce aldehydes, ketones, and acids (see also Section 9.6.2). The peroxy borates so formed then are hydrolyzed to yield the alcohol. The carbon atoms at the chain ends are largely immune to oxidation, so the product consists predominantly of isomeric secondary alcohols. The reaction does not stop at... 

Furost-20(22)-enes (384) react with peroxy-acid with introduction of a hydroxy-group at the 20a-position, and ring closure to give the 20a-hydroxy-spirostan (385). The isolation of up to 25% of the 20,23-diol (386) is attributed to contamination of the furost-20(22)-ene with the 22(23)-unsaturated isomer. Almost all 3,5-dienolic esters and ethers react with electrophiles at C-6, apart from rare instances of reaction at C-4 or C-2 (see above). Reaction between the dienolic ethers (387) and tetranitromethane in ether has now been shown to afford the 2 -nitro-derivatives (388). No mechanistic details are available, but it is tempting to suggest the involvement of free-radicals derived from the reagent. 

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