Solvents 3-methyl-2-oxazolidinone

A stirred solution of 2.9 g (4S,5R)-5-methyl-2-oxazolldmone-4-carboxylic acid (20 mmol) in 500 mL 0.02 N NaOAc/MeOH was electrolyzed at room temperature under galvanostatic conditions using graphite electrodes (3 x 30 x 100 mm) in an undivided cell. After consumption of 3F/mol at a current density of 5 mA/cm, the solvent was evaporated, the white residue was purified, and the diasteromers were separated by Hash chromatography on silica gel with Et20 as the eluent to afford 2.1 g (4R/S,5R)-4-methoxy-5-methyl-2-oxazolidinone as white crystals, in a yield of 88%, m.p. 87-90°C. The (4R,5R)-4-methoxy-5-methyl-2-oxazolidinone was formed with 77% ds. 

Methyl-2-oxazolidinone (NMO) is isostructural with EC with an N-CH3 group substituted for one of the EC ring oxygen atoms. It is a highly polar solvent (er=78 at 25 °C) and was once used in primary lithium cells [54]. However, its oxidation potential on a glassy carbon is much lower than that of PC [55]. To increase its... 

Typical procedure. (4S,5R)-5-Methyl-2-oxazolidinone-4-carboxylic acid 587 [415] To a solution of L-threonine (2.38 g, 20 mmol) and a trace of thymolphthalein as indicator in 2 N NaOH (30 mL) at 0 °C, methyl chloroformate (2.4 mL, 30 mmol) was added dropwise. To maintain pH 10, it was necessary to add further portions of NaOH at intervals. The solution was allowed to slowly warm to room temperature and was stirred overnight. The reaction mixture was then neutralized with dilute HCl. After evaporation of the volatiles, a white precipitate was obtained. The product was extracted with ethyl acetate (250 mL), which was acidified with HCl. The solvent was again evaporated and the white product was recrystallized from ethyl acetate/petroleum ether (40/60) to afford 2.18 g (75%) of oxazolidinone 587. 

Typical procedure. (4R,5S)-4-MethYl-5-phenyloxazolidin-2-one [487] To a solution of (IS,2J )-norephedrine (40 g, 0.26 mol) in toluene (400 mL) was added diethyl carbonate (37 mL, 0.32 mol). The mixture was heated to reflux (under Ar) while 40 mL of solvent was removed through the use of a Dean-Stark apparatus. The mixture was allowed to cool for 20 min, and then sodium methoxide (1 g) was added. Upon reheating, an EtOH/toluene azeotropic mixture was removed at 75-77 °C. After 3 h, the reaction was complete and the temperature of the mixture had increased to 125 °C. The mixture was left to stand at room temperature for 16 h, whereupon (4R,5S)-4-methyl-5-phenyloxazdidin-2-one 40.6 g) crystallized and could be collected. The solvent was removed from the filtrate in vacuo and the residue was redissolved in EtOAc (250 mL). This solution was washed with brine (50 mL) and a precipitate was removed by filtration. The solvent was then removed in vacuo and toluene (50 mL) was added to the residue. Removal of the toluene by distillation yielded oily crystals of the oxazolidinone, which were washed with Et20 to afford 4.5 g (total 45 g, 97%). 

Our attempts to obtain a crystalline oxazolidinone were eventually successful with the (L)-iV-i-butoxycarbonyl derivatives and 4 -biphenylcarboxaldehyde, leading to 29d,[26] In solution, flie typical 85 15 equilibrium ratio of cis and trans diastereomers is observed (Table I, entry 4), When the solvent was partially removed and the residue suspended in teft-butyl methyl ether, an off-white solid precipitated, which consists of pure cw-29d in 88% yield. Analysis of the mother liquors shows very minor amounts of cis and trans product in a 85 15 ratio, along with some unreacted carbamate and a,a-dichloro biphenyl. The presence of both cis and trans isomers in the mother liquor is clear evidence that a crystallization-induced asymmetric transformation is responsible for the high selectivity. 

Table 11.1 Organic carbonates and esters as electrolyte solvents [1] with EC ethylene carbonate, PC propylene carbonate, BC butylene carbonate, yBC y butylene carbonate, yVC y-valerolactone, NMO Af-methyl-2-oxazolidinone, DMC dimethyl carbonate, DEC diethyl carbonate, EMC ethyl methyl carbonate, EA ethyl acetate, MB methyl butyrate, EB ethyl butyrate...

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