(4R)-Ethyl 4-(4-chloro-phen-yl)-2-hydr-oxy-5-oxo-2,3,4,5-tetra-hydro-pyrano[3,2-c]chromene-2-carboxyl-ate.

The title compound, C(21)H(17)ClO(6), is optically pure and adopts an R configuration. It was obtained by an organocatalytic asymmetric Michael addition of 4-hydroxy-coumarin with (E)-ethyl 4-(4-chloro-phen-yl)-2-oxobut-3-enoate. The structure consists of a tetra-hydro-pyran unit fused to the coumarin ring ring system. The hydroxyl and phenyl groups are on the same side of the tetra-hydro-pyrane ring. The benzene ring is almost perpendicular to the coumarin ring [dihedral angle of 72.89 (3)°]. In the crystal structure, inter-molecular O-H⋯O hydrogen bonds are observed. An intra-molecular O-H⋯O contact also occurs.