A novel glycoside lactone derivative with a 2-C-unsaturated diester substituent

The title 4,6-O-benzyl­idene-α-d -gluco­pyran­oside (systematic name: methyl 4-methoxy-2-oxo-8-phenyl-1,2,5a,6,9a,9b-hexa­hydro-4H,8H-7,9-dioxa­cyclo­penta­[c]­chromene-3-carboxyl­ate), C₁₈H₁₈O₈, has been synthesized from the reaction of methyl 4,6-O-benzyl­idene-α-d -2-ketogluco­pyran­oside with diethyl or di­methyl malonate. The compound adopts a chair–chair conformation. The newly formed five-membered ring is fused to the gluco­pyran­oside ring along the C₂—C₃ bond and is planar with an r.m.s. deviation of 0.0091 Å.