Chloroform → 1-oxoheptyl-D-allo-Threonine

A solution of n-heptanoyl chloride (440 mL, 2.83 mol) in THF (250 mL) is added dropwise, over a period of 30 min, to a cold (-5 to 0° C.), vigorously stirred mixture of D-allo-Thr (300 mg, 2.51 mmol) and 2N aq. NaOH (3.5 mL, 7.0 meq) in THF (4.0 mL). The resulting mixture is stirred for 2 h at the same temperature and overnight at room temperature. The volatiles are removed and the residue is diluted with water and acidified, using conc. HCl. The mixture is extracted with EtOAc and the combined organic solution is washed with brine, dried, filtered, and concentrated to provide crude 2c-1 (420 mg, containing 10% excess heptanoyl reagent) which solidifies upon standing. NMR δ1.28 (d, J=6.5, 3H), 4.20 (m, 1H), 4.61 (dd, J=3.4, 6.6, 1H), 6.56 (br d, J=6.9, 1H); [α]D26 -38±2 (CHCl3).