Useful sialic acid modifications catalyzed by palladium

A stereo- and regioselective allylic substitution on simple N-acetylneuraminic acid (Neu5Ac2en) derivatives that ensures the control of the regio- and stereoselectivity and affords the C-2 or C-4 products with high efficiency, was studied. The Neu5Ac2en substrates were easily prepared from the peracetylated methyl ester 9 obtained by standard treatment overnight of the corresponding Neu5Ac methyl ester. Treatment of acetate 10 under Pd⁰-catalyzed allylic substitution conditions using sodium dimethylmalonate as a nucleophile failed to provide any alkylation product. The regioselectivity was largely improved to a synthetically useful level when using a more basic monophosphine ligand. A complete reversal of the regioselectivity occurred when the reaction was performed in the presence of bidentate phosphine. Selective transformations of these products provide easy entry to a variety of modified sialic acid derivatives, which can serve as useful sialyl building blocks for biological research.