Tetrahydrofuran → 4-Benzyloxy-2-((S)-2-hydroxy-propylamino)-benzaldehyde

To a solution of the product of Step B (19.3 g, 68.3 mmol) in a mixture of anhydrous cyclohexane and THF (200 mL, 40 mL) at 0° C. under nitrogen was added diisobutylammonium hydride (1 M solution in hexane, 239 mL, 239 mmol) over 30 min. This mixture was stirred 18 h at ambient temperature, additional diisobutylammonium hydride (40 mL, 40 mmol) was added, and the mixture was stirred an additional 24 h. The reaction mixture was cooled on an ice bath and the reaction was quenched by the addition of MeOH (exothermic) and 2 N HCl to maintain a pH of 1. The mixture was extracted with EtOAc (3×300 mL) and the extracts were dried and concentrated to a brown oil (18.5 g). The crude oil was triturated with EtOAc/hexane, and filtered to give an oil (16.1 g, 83% crude yield). A small portion of this material was purified by chromatography (silica, 20% to 50% EtOAc/hexane) to afford a solid; mp 68-69° C.