ABOUT THE RADICAL MECHANISM OF THE OXIDATIVE COUPLING OF THE DIANIONS OF CARBOXYLIC-ACIDS - COMPETITION BETWEEN NUCLEOPHILIC-SUBSTITUTION AND ELECTRON-TRANSFER

Evidence is provided for the radical nature of the oxidative coupling of dianions of unsaturated caboxylic acids, as it can be carried out by oxidation with an electron transfer reagent; namely p-dinitrobenzene. Oxidative coupling by iodine does not occur through iodoacids as intermediates, as this oxidation leads to acids 2 and 3 in a regioselectivity ratio gamma gamma/alpha gamma inverted to that obtained on reaction of the lithium salt of iodoacid 4 with the dianion of crotonic acid. Reaction of the dianions with some arylmethyl bromides and with 1,3-diiodopropane afford both alkylation and oxidative coupling products, as an example of competition between nucleophilic substitution and electron transfer.