C9H12O3, Mr = 168.2, triclinic, P1, a = 5.5385 (6), b = 8.543 (1), c = 10.373 (1) A, alpha = 113.329 (9), beta = 100.78 (1), gamma = 99.82 (1) degree, V = 426.2 (2) A3, Dx = 1.31 g cm-3, Z = 2, Cu K alpha (lambda = 1.54178 A, graphite monochromator), mu = 8.2 cm-1, F(000) = 180, T = 293 K. Final R = 0.036, wR = 0.081 for 1559 reflections with I greater than 3 sigma(I). The relative configurations at the two chiral centers are (S,R). The dihedral angle between the five- and six-membered rings (O1--C4--C5--O3) is 69.9 (1) degree. The tetrahydropyran is in a chair conformation with the furanone ring equatorial.