Remarkable substituent effects on the oxidizing ability of triarylbismuth dichlorides in alcohol oxidation

Substituent effects on the oxidizing ability of triarylbismuth dichlorides were examined by intermolecular and intramolecular competition experiments on geraniol oxidation in the presence of DBU. It was found that the oxidizing ability of the dichlorides increases with increasing electron-withdrawing ability of the para substituents, and by introduction of a methyl group at the ortho position of the aryl ligands attached to the bismuth. The intermolecular and intramolecular H/D kinetic isotope effects observed for the competitive oxidation of p-bromobenzyl alcohols indicate that the rate-determining step involves C-H bond cleavage. Several primary and secondary alcohols were oxidized efficiently under mild conditions by the combined use of newly developed organobismuth(V) oxidants and DBU.