N-But-oxy-carbonyl-5-oxo-l-proline ethyl ester.

The mol-ecular structure of the title compound, C12H19NO5, may be visualized as made up of two nearly perpendicular planes [dihedral angle = 87.39 (12)°] and its crystal structure is a good example of C-H⋯O inter-actions assuming significance in optimizing supra-molecular aggregation in crystals in a mol-ecule which is severely imbalanced in terms of donors to acceptor atoms. The pyrrolidine ring adopts a ((3) T 2) twist conformation with puckering parameters Q = 0.2630 (4) Å and ϕ = 59 (9)°. The crystal structure features R 2 (4)(10) and R 3 (4)(26) ring motifs formed by four weak C-H⋯O inter-actions, leading to supra-molecular sheets lying parallel to the bc plane.