The title 4,6-O-benzylidene-alpha-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), C(18)H(18)O(8), has been synthesized from the reaction of methyl 4,6-O-benzylidene-alpha-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 C(2)--C(3) bond and is planar with an r.m.s. deviation of 0.0091 A.