A pimpinellin monomer and dimer isolated from the roots of Esenbeckia grandiflora.

X-ray diffraction studies carried out on single crystals of the monomeric, viz. 5,6-dimethoxy-2H-furo[2,3-h][1]benzopyran-2-one, C(13)H(10)O(5), and dimeric, viz. 5,5',6,6'-tetramethoxy-3,3',4,4'-tetrahydro-2H,2'H-3,3':4,4'-bi(furo[2,3-h][1]benzopyran)-2,2'-dione, C(26)H(20)O(10), forms of pimpinellin have revealed that, following cyclodimerization, the carbonyl groups are head-to-head with respect to one another. In the monomer, the heterocyclic ring is planar, but it exhibits a twisted-boat conformation in the dimer. Both the monomer and the dimer interact through C-H...O interactions.