[OH:1][NH:2][C:3]1([C:11]#N)[CH2:8][CH2:7][N:6]([O:9][CH3:10])[CH2:5][CH2:4]1.S(=O)(=O)(O)[OH:14].[CH3:18][OH:19]>ClCCl>[CH3:18][O:19][C:11]([C:3]1([NH:2][OH:1])[CH2:8][CH2:7][N:6]([O:9][CH3:10])[CH2:5][CH2:4]1)=[O:14]To a suspension of 4-hydroxyamino-1-methoxy-piperidine-4-carbonitrile (230 g, 1.34 mol) in dichloromethane (2400 ml) at room temperature was added concentrated sulfuric acid (358 ml, 658.8 g, 6.72 mol) dropewise, and the reaction mixture was stirred at 40° C. for one hour. Methanol (925.1 ml, 731.7 g, 22.8 mol) was added at 40° C. dropewise, and the mixture stirred at 40° C. for 4 hours. The dichloromethane was distilled off allowing to heat the reaction mixture at 60° C. for 24 hours. The reaction mixture was poured on ice (3 kg) and neutralized by careful addition of concentrated aqueous sodium hydroxide first, followed by saturated aqueous sodium hydrogen carbonate. The aqueous phase was saturated with sodium chloride, extracted with ter-butyl methyl ether (10×300 ml), the combined organic layers washed with brine, dried over sodium sulfate and concentrated to afford a first crop of product (163.8 g). Further extraction of the aqueous layer with ethyl acetate delivered another 35 g of crude product. Yield: 198.8 g of 4-hydroxyamino-1-methoxy-piperidine-4-carboxylic acid methyl ester as a red-brown, viscous oil. This material was used without further purification in the next step.
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