Michael reactions on conformationally flexible methyl 3-C-nitro-hex-2-enopyranoside derivatives

Dimethyl malonate and dibenzoylmethane attacked the C-2 position of the title 3-nitro-2-enopyranosides from the side opposite the anomeric methoxyl group to afford the 3-enopyranosides (SN2′ products). In the case of 2,4-pentanedione and ethyl acetoacetate, further intramolecular cyclization occurred to yield dihydropyran derivatives.