[Na].[CH2:2]([O:9][N:10]1[C:16](=[O:17])[N:15]2[CH2:18][C@H:11]1[CH2:12][CH2:13][C@H:14]2[C:19](O)=[O:20])[C:3]1[CH:8]=[CH:7][CH:6]=[CH:5][CH:4]=1.CN1CCOCC1.ClC(OCC)=O.[BH4-].[Na+]>O1CCCC1.C(OCC)(=O)C.O>[CH2:2]([O:9][N:10]1[C:16](=[O:17])[N:15]2[CH2:18][C@H:11]1[CH2:12][CH2:13][C@H:14]2[CH2:19][OH:20])[C:3]1[CH:4]=[CH:5][CH:6]=[CH:7][CH:8]=1The sodium salt of (2S, 5R)-6-benzyloxy-7-oxo-1, 6-diaza-bicyclo [3.2.1] octane-2-carboxylic acid (II) (50 g, 0.16 moles, prepared as per the procedure described in Indian Patent Application No. 699/MUM/2013) was suspended in tetrahydrofuran (500 ml). To the suspension was added N-methyl morpholine (18.4 ml, 0.16 moles) under stirring. The reaction mixture was cooled to about −10° C. and ethyl chloroformate was added via addition funnel and stirred for 1 hour at about −10° C. To the reaction mixture was added NaBH4 (9.56 g, 0.25 moles) in lots under stirring. The reaction was monitored with the help of thin layer chromatography (TLC). After completion of reaction, water (500 ml) followed by ethyl acetate (500 ml) was added to the reaction mass. The reaction mixture was stirred for 30 minutes and the layers were separated. Organic layer was washed with brine (200 ml). The solvent was evaporated under vacuum to dryness to provide 43 g of (2S, 5R)-6-(benzyloxy)-2-(hydroxymethyl)-7-oxo-1,6-diaza-bicyclo[3.2.1] octane (III) as a pale yellow oil (99% yield).
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