ABOUT THE RADICAL MECHANISM OF THE OXIDAT IVE 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 b y oxidation with an electron transfer reagent; namely p-dinitrobenzene . Oxidative coupling by iodine does not occur through iodoacids as int ermediates, as this oxidation leads to acids 2 and 3 in a regioselecti vity ratio gamma gamma/alpha gamma inverted to that obtained on reacti on 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 ele ctron transfer.