[ClH:1].C(OC([N:9]1[CH2:13][CH2:12][C@@H:11]([S:14][CH2:15][C:16]2[CH:21]=[CH:20][C:19]([O:22][CH3:23])=[CH:18][CH:17]=2)[CH2:10]1)=O)(C)(C)C>C(OCC)(=O)C.C(OC(C)C)(C)C>[ClH:1].[CH3:23][O:22][C:19]1[CH:18]=[CH:17][C:16]([CH2:15][S:14][C@H:11]2[CH2:12][CH2:13][NH:9][CH2:10]2)=[CH:21][CH:20]=1106 ml of a 4N ethyl acetate solution of hydrogen chloride were added, whilst ice-cooling, to a solution of 27.50 g of (3R)-1-t-butoxycarbonyl-3-(4-methoxybenzylthio)pyrrolidine [prepared as described in step (2) above] dissolved in 100 ml of ethyl acetate, and the mixture was stirred at 0° to 5° C. for 30 minutes and then at 25° C. for 2 hours. At the end of this time, the mixture was diluted with 200 ml of diisopropyl ether, and the crystals which precipitated were collected by filtration, to give 20.84 g of the title compound as colorless crystals, melting at 125°-126° C.
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