NONCHAIN PROCESSES IN NUCLEOPHILIC SUBSTITUTIONS TRIGGERED BY ELECTRON-TRANSFER (S(RN)1) - PHOTOCHEMICAL AND ELECTROCHEMICAL INDUCTION OF THE SUBSTITUTION OF 1-IODOADAMANTANE BY ARENETHIOLATE IONS

Photochemical induction of the reaction of 1-iodoadamantane with arene thiolate ions provides a clear-cut example of nonchain S(RN)1 substitu tions. With 4-methoxy-, 4-methyl-, and 4-cyanobenzene and benzenethiol ate ions, excellent yields (over 85%) are obtained in spite of efficie nt electron transfer quenching of the very easily oxidized anion radic al of the substituted product by quaternary ammonium countercations. T he production of the corresponding disulfides is used to determine the number of chains. Absorption and fluorescence spectroscopy and laser pulse irradiation experiments indicate that the electron which trigger s the substitution process is generated by photoejection from the nucl eophile, with an efficiency that decreases in the order 4-methoxybenze ne > 4-methylbenzene > 4-benzene > 4-cyanobenzenethiolate. Electron ph otoejection does not occur with naphthalenethiolate ions. However subs titution can be entrained by addition of benzenethiolate ions. The two nucleophiles were found to have comparable reactivities toward the 1- adamantyl radical. Rather than the formation of its anion radical, the first step of the S(RN)1 process is a dissociative electron transfer to 1-iodoadamantane, yielding directly the adamantyl radical. This is the reason that direct electrochemical induction of the substitution w as not observed. Induction by electrogenerated aromatic anion radicals could be observed. It was much less efficient than photoinduction bec ause the amount of electron donor species required to trigger the reac tion is much larger.