The electrolyses of bromoalkyl acrylates were carried out in N,N-dimethylfo
rmamide in the presence of a catalytic amount of heptamethyl cobyrinate per
chlorate under various reaction conditions. A large-membered cyclic lactone
was obtained in a moderate yield. A photo-sensitive intermediate having a
cobalt-carbon bond formed during the electrolysis has been characterized us
ing electronic and electrospray ionization mass spectroscopies in the dark.
The formation of a cyclic lactone was inhibited by the addition of the spi
n-trapping reagent, a-phenyl N-(t-butyl)nitrone. Based on various spectrosc
opic results. the electrolysis proceeds as follows: the Co(II) complex as a
catalyst is electrochemically reduced to the Co(I) species, and the corres
ponding alkylated complex is generated by the reaction of the supernucleoph
ilic Co(I) species with a bromoalkyl acrylate. The alkylated complex is sub
sequently decomposed to form the substrate radical, and the intramolecular
addition of the radical affords the cyclic product. During the catalytic re
action, the cobalt complex repeatedly acts as a mediator. (C) 2001 Elsevier
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