3-tert-Butyl-2-oxo-1-oxaspiro-[4.5]dec-3-en-4-yl 4-chloro-benzoate.

The title tetronic acid derivative, C(20)H(23)ClO(4), which is a spiro-diclofen analogue, has two crystallographically independent mol-ecules in the asymmetric unit (Z' = 2). The cyclo-hexane rings in the respective mol-ecules A and B adopt chair conformations [four C atoms are planar with mean deviations of 0.013 (2) and 0.001 (2) Å, and the flap positions deviate by 0.653 (4) and -0.663 (3) Å (mol-ecule A) and 0.642 (4) and -0.643 (5) Å (mol-ecule B) from the plane]. The furan ring makes dihedral angles of 86.9 (1) (mol-ecule A) and 85.4 (1)° (mol-ecule B) with the respective benzene rings.