In the title compound {systematic name: N-[(4R,5R)-3,11-dioxo-10-oxa-6-thia-2-aza-tricyclo-[6.3.0.0(2,5)]undec-1(8)-en-4-yl]-2-phenyl-acetamide}, C(16)H(14)N(2)O(4)S, the four- and five-membered rings adopt planar conformations (with r.m.s. deviations of 0.0349 and 0.0108 Å respectively) while the six-membered ring adopts a half-chair, or envelope-like, conformation with the S atom in the flap position. In the crystal, mol-ecules are linked by N-H⋯O hydrogen bonds.