(Z)-2-(2-oxopyrrolidin-1-yl)but-2-enoic acid

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: A1 l flask fitted with a magnetic stirring bar and a Dean-Stark trap was charged with 2-oxobutanoic acid (25 g, 245 mmol), toluene (500 ml, 20 vol) and 2-pyrrolidinone (37.2 ml, 490 mmol, 2 equiv). The reaction mixture was stirred under reflux with azeotropic removal of water via the Dean-Stark trap for 5.5 hours. The solution was then concentrated to ca. 90 ml (3.6 vol) and allowed to cool slowly to ambient temperature. Off-white solid started to come out of solution at around 55° C. The solid was filtered, the cake was washed with toluene (2×1 vol) followed by dichloromethane (3×1 vol) and dried on the filter under vacuum for 5 min to afford crude material (28 g, 70% yield). The crude product was dissolved in acetone (450 ml, 16 vol) at reflux, cooled slowly to ambient temperature and allowed to crystallise over 12 hrs at −15 to −20° C. Pure product was obtained as a white crystalline solid (21 g, 51% overall yield). The solution was then concentrated to ca. 90 ml (3.6 vol) to come out of solution at around 55° C The solid was filtered the cake was washed with toluene (2×1 vol) dried on the filter under vacuum for 5 min