Reaction Steps
To a solution of (1S,2R,5R,6S)-2-acetylamino-3-oxo-bicyclo [3.1.0] hexane-2,6-dicarboxylic 2-benzyl ester 6-ethyl ester (XVI) (77 mg, 0.214 mmol) in EtOH (2 mL) and THF (1 mL) was added LiBH4 (5 mg, 0.23 mmol) at -50° C. and the mixture was stirred at -50° C. for 45 min. The reaction was quenched by addition of 1 N HCl (ca. 0.5 mL), warming up to 23° C. and stirring for 10 min. After dilution with ethyl acetate and extraction with sat. NaHCO3 -sol., brine and drying over MgSO4 the crude product was purified by silica gel column chromatography with toluene/acetone 3:1 to give (1S,2R,3R,5R,6S)-2-acetylamino-3-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 2-benzyl ester 6-ethyl ester (XVII) (33 mg, 43%, less polar product) as a colorless oil and (1S,2R,3S,5R,6S)-2-acetylamino-3-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 2-benzyl ester 6-ethyl ester (XVIII) (35 mg, 45%, more polar product) as a white solid. (XVII): 1H-NMR (250 MHz, CDCl3) □1.26 (3H, t, J=7.2 Hz), 1.76 (1H, t, J=3.5 Hz), 2.07 (1H, m), 2.10 (3H, s), 2.16 (1H, dd, J=6.1, 3.0 Hz), 2.30-2.41 (3H, m), 3.97-4.13 (3H, m), 5.24 (2H, bs), 6.19 (1H, bs), 7.26-7.38 (5H, m); MS[ISP] 362 (M+H+); □D20 -11.24° (c=1.18, CHCl3). (XVIII): 1H-NMR (250 MHz, CDCl3) □1.25 (3H, t, J=7.1 Hz), 1.98 (1H, m), 2.05-2.11 (1H, m),2.06 (3H, s), 2.18 (1H,t,J=3.5 Hz), 2.27-2.41 (2H, m), 2.59 (1H, ddd,J=13, 7, 5 Hz), 4.12 (2H, m), 4.68 (1H, dd, J=7, 5 Hz), 5.17 (2H, s), 6.30 (1H, bs), 7.26-7.40 (5H, m); MS[ISP] 362 (M+H+); mp 145-147° C.; □D20 +42.44° (c=1.01, CHCl3).
