To a solution of (1S,2R,3R,5R,6S)-2-azido-3-hydroxy-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 2-benzyl ester 6-ethyl ester (VII) (200 mg, 0.58 mmol) and allyl 2,2,2-trichloroacetimidate (0.18 mL, 1.16 mmol) in cyclohexane (0.7 mL) was added TfOH (29 □L), whereupon the solution became hot and stirring was continued at 23° C. for 1 h. The reaction mixture was poured on ice, diluted with ether, washed with sat. NaHCO3 -sol., brine and dried over MgSO4. The crude product was purified by silica gel column chromatography with hexane/EtOAc 4:1 to give (1S,2R,3R,5R,6S)-3-allyloxy-2-azido-bicyclo [3.1.0]hexane-2,6-dicarboxylic acid 2-benzyl ester 6-ethyl ester (XXIII-2) (31 mg, 14%) as a yellow oil. 1H-NMR (250 MHz, CDCl3) □1.26 (3H, t, J=7.1 Hz), 1.76 (1H, t, J=3.5 Hz), 2.03-2.26 (3H, m), 2.32 (1H, dd, J=12, 7 Hz), 3.58 (1H, dd, J=9, 7 Hz), 3.92 (1H, m), 4.02 (1H, m), 4.13 (2H, q, J=7.1 Hz), 5.10-5.22 (2H, m), 5.25 (1H, d,J=12 Hz), 5.34 (1H, d,J=12 Hz), 5.75 (1H, m), 7.30-7.42 (5H, m);MS[EI] 284 [(M-CO2Et-N2)+ ]; □D20 17.85° (c=0.50, CHCl3).
