To a 500 mL round-bottomed flask was added benzyl 5-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxylate (3.1 g, 10 mmol), chlorobenzene (30 mL) and the mixture cooled in an ice bath. The trimethylaluminum (25 ml, 50 mmol) was added and the ice bath removed followed by the addition of (S)-2-methyloxirane (0.87 g, 15 mmol). The mixture stirred 1 h and cooled in an ice bath with the addition of THF (60 mL). Sodium sulfate decahydrate (3g) was added to the mixture cautiously (foaming) and the mixture stirred 1 h. Sodium sulfate (10 g) was added and stirred 1 h. The mixture was filtered through celite, washed with 4:1 chloroform/isopropanol and the filtrate concentrated, diluted with chloroform, washed with 1 N HCl and sat. sodium bicarbonate. The organic layer was dried over sodium sulfate and concentrated. The crude product was purified by silica gel chromatography eluting with methanol/chloroform to afford the title compound as a foam (1.5 g). MS (ESI pos. ion) m/z: 367 (MH+). Calc'd exact mass for C21H22N2O4: 366.
