Reagents and conditions (i) CDI, THF, 99%; (ii) POCl3, CH2Cl2, reflux, 87%; (iii) NaBH4, MeOH, −78 °C, 77%; (iv) HCHO, Na(OAc)3BH, DCM, 95%; (v) PIFA, BF3.OEt2, HFIP, rt, 45 min, 16% (vi) (−)-2,3-Di-p-toluoyl-L-tartaric acid, EtOH then 10% aq. NaOH, 30%, 96% ee (vii) (+)-2,3-Di-p-toluoyl-D-tartaric acid, EtOH then 10% aq. NaOH, 32%, 97% ee