Unexpected C-H bond activation mediated by gold(III) acetate

Reaction of gold(III) acetate with 6-ethyl-2,2 '-bipyridine resulted in an unexpected Csp3-H bond functionalization of the ethyl substituent, leading to 1-(2,2 '-bipyridin-6-yl)ethylacetate (1) by formal substitution of a hydrogen by an acetate group. The analogous reaction on 6-methyl-2,2 '-bipyridine gave a mixture of mono-and di-substituted products (1-(2,2 '-bipyridin-6-yl)methylacetate and 1,1 '-(2,2 '-bipyridin-6-yl)dimethylacetate, 2 and 4) in addition to the corresponding aldehyde 2,2 '- bipyridine-6-carbaldheide. In contrast, reaction of 2-ethylpyridine and 6-(1-methylbenzyl)-2,2 '-bipyridine under the same experimental conditions did not give functionalization of the substituent. The synthesis of the bipyridyl monoacetates 1 and 2 has already been reported using different methods; in contrast the di-acetate 4 was never reported. A detailed characterization of 1 by means of one-and two-dimensional NMR spectroscopy has also been completed. These results furnish new information on the ability of gold(III) to activate and functionalize organic fragments in uncommon positions. To the best of our knowledge, this is the first report of Au(OAc)3 mediating C-H functionalization at the alpha-position of bipyridine alkyl substituents.