Thionyl Chloride → alpha-Chloro-2-nitrobenzenepropanoic acid 2,6-dimethylpiperidine salt

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To magnetically stirred N,N-dimethylformamide (3 mL) cooled in ice was added slowly dropwise thionyl chloride (4.5 ml., 61.7 mmol) and the resulting cold Vilsmeier reagent was diluted with dichloromethane (30 ml.). (-)-α-Hydroxy-2-nitrobenzenepropanoic acid [3.00 g., 14.2 mmol, [α]D25 -63.04° (c 0.955, 95% ethanol)] in dichloromethane (70 ml.) was added. The resulting solution, protected from moisture, was left at room temperature (25° overnight. The solution was added to stirred ice and the mixture was stirred for 1 hour, during which time it warmed to room temperature. The dichloromethane solution was separated and washed thrice with water and dried (MgSO4). Evaporation gave a syrup which was subjected to an oil pump vacuum for 1.5 hours. The syrup was dissolved in ether and 2,6-dimethylpiperidine was added to approximate neutrality (pH 9 with pH paper). The crude titled product [2.98 g. (61%), m.p. 155°-158° C. dec.] crystallized readily. Two crystallizations (methanol-ether) with decolorization (Nuchar C-190N) gave 1.91 g. (39%) of pure product; m.p. 164°-167° C. dec., [α]D25 +42.11° (c 1.09, 95% ethanol).

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