rac-Ethyl 2-hy­droxy-2,7,7-trimethyl-4-(4-nitro­phen­yl)-5-oxo-3,4,5,6,7,8-hexa­hydro-2H-chromene-3-carboxyl­ate

The title mol-ecule, C21H25NO7, has four stereogenic centres and crystallized as a racemate. It consists of enanti-omeric pairs with the relative configuration rac-(1R*,2S*,3R*). The cyclo-hexenone ring adopts an envelope conformation; the dimethyl-substituted C atom lies 0.640 (1) Å out of the mean plane formed by the rest of the ring atoms (r.m.s. deviation = 0.016 Å). The oxacyclo-hexene ring adopts a half-chair conformation, the hy-droxy- and carboxyl-substituted C atoms lying -0.336 (1) and 0.419 (1) Å, respectively, out of the mean plane formed by the rest of the ring atoms (r.m.s. deviation = 0.002 Å). In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into a chain along the c-axis direction.