Crystallization of 6-hydroxy-2,2-dimethyl-5-[2-oxo-5-(pyrrolidin-1-yl)cyclo
pent-3-en-1-yl]-4H-1,3-dioxin-4-one from aqueous hydrobromic acid gave the
title compound, C12H16BrNO5.H2O. The crystal structure is stabilized by a t
hree-dimensional network of hydrogen bonds.