Oxidative radical cyclizations of malonate enolates induced by the ferrocenium ion - a remarkable influence of enolate counterion and additives

To generalize oxidative radical cyclizations of malonate enolates induced b y recyclable single electron transfer (SET) oxidant ferrocenium hexafluorop hosphate 1, the reactivity of a series of enolates 3 that differ only in th eir counterions was studied. Only lithium enolates were oxidized by 1, irre spective of their generation method. The presence of amines in stoichiometr ic or substoichiometric amounts is necessary for SET oxidation-bicyclizatio n of Na, K. Mg. Zn, Si, or Ti enolates 3. The nucleophilicity of 3, the ami ne, and the presence of halide ions determine the bicyclization yield of la ctone 7.