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

Abstract

To generalize oxidative radical cyclizations of malonate enolates induced by recyclable single electron transfer (SET) oxidant ferrocenium hexafluorophosphate 1, the reactivity of a series of enolates 3 that differ only in their counterions was studied. Only lithium enolates were oxidized by 1, irrespective of their generation method. The presence of amines in stoichiometric or substoichiometric amounts is necessary for SET oxidation–bicyclization of Na, K, Mg, Zn, Si, or Ti enolates 3. The nucleophilicity of 3, the amine, and the presence of halide ions determine the bicyclization yield of lactone 7.