Effects of Silver Carbonate and p-Nitrobenzoic Acid for Accelerating Palladium-Catalyzed Allylic C-H Acyloxylation.

An allylic C-H acyloxylation of terminal alkenes with 4-nitrobenzoic acid was assisted by a bidentate-sulfoxide-ligated palladium catalyst combined with 1,4-benzoquinone and Ag2CO3 under mild reaction conditions. The catalytic activity was remarkably enhanced by Ag2CO3 as an additive and 4-nitrobenzoic acid as a carboxylate source; both components were essential to exhibiting high catalytic activity, high branch selectivity, and a wide substrate scope with low loading of the palladium catalyst. Branch-selective allylic acyloxylation of ethyl 7-octenoate (1a) gave the product which was led to ethyl 6,8-dihydroxyoctanoate (5), a useful synthetic intermediate of (R)-α-lipoic acid.