The aminoacetonide 2.87g (Acros, 10.5 mmol) and triethylamie 2.5mL (18 mmol) was dissolved in dichloromethane 20mL and Cbz-OSu 2.617g (10.5 mmol) was added in one portion with cooling on ambient bath (exothermic). The mixture was stirred for 1 hour, then portioned between ethyl acetate 150mL and sat. bicarbonate 100mL. The organic phase was washed with additional sodium bicarbonate (100mL) and aqueous phases re-extracted with ethyl acetate (150mL). Combined organic extracts dried (MgSO4) and evaporated. The residue was dried on highvac. The obtained crude Cbz-protected acetonide ester (4.38g) was dissolved in dichloromethane 15mL, TFA 10mL was added, the mixture was stirred for 40 min then evaporated and dried on higvac. The residue was purified on a column of silica (150g) in a mix dichloromethane-ethyl acetate 1:2 (2 parts of EtOAc:1 part DCM, 4L total). Y=1.875g (61%) of a white crystalline solid.
1H(d6-DMSO, 400MHz): 7.343(m, 5H), 5.204(br s, 1H), 5.003(s, 2H), 4.615(m, 1H), 4.097(br s, 1H), 3.117(m, 2H), 2.623(ddAB, 17.3Hz, 12.6Hz, 1H), 2.368(m, 1H), 1.766-1.663(m, 4H)