In the title compound, C21H20BrNO4S, a key intermediate in the synthesis of the widely used β-lactamase inhibitor tazobactam, the five-membered thiazolidine ring adopts an envelope conformation and the four-membered azetidine ring is in a distorted planar conformation. The crystal structure features C—H...O hydrogen bonds and a weak C—H...π interaction.
