Décomposition du percarbonate deO,O‐t‐butyle etO‐isopropényle en solution: Acétonylation des esters, acides et nitriles

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Abstract
The Free‐Radical Decomposition ofO,O‐t‐Butyl andO‐Isopropenyl Peroxycarbonate in Solution: the Acetonylation of Esters, Acides and NitrilesThe free‐radical decomposition ofO,O‐t‐butyl andO‐isopropenyl peroxycarbonate in substratres possessing mobile H‐atoms (SH) consists mainly in an induced chain process leading to acetonylated derivatives of the solvent. Fairly good yields are obtained but teh acetonylation of functional substrates often gives mixtures of isomers.In the case of methyl acetate, the acetonylation occurs on the C‐atoms adjacent to the carbonyl (acylox moiety) and to the O‐atom (alkox moiety). However, the relative amounts of the isomeric products depend on the concentration of the peroxycarbonate solutions; at lowest concentration, methyl 4‐oxopentanoate (acyloxy moiety) is obtained selectively. It is assumed that the free radicals issued from the solvent are able to abstract H‐atoms of other molecules of solvent before adding to the double bond of the peroxycarbonate; the more the peroxycarbonate solution is diluted the more the transfers from the C‐atom adjacent to the carbonyl to the radicals adjacent to the O‐atom are favoured. In the case of methyl alkanoates, H‐transfers from the α‐C‐atoms to β‐radicals of teh acyloxy moiety may account for the orientation of the process. Owing to similar H‐transfer processes, the acetonylation of functional esters, of acids and nitriles is selective in most cases.