5-{4-[2-hydroxy-2-(3-methoxyphenyl)ethoxy]benzylidene}-1,3-thiazolidine-2,4-dione (1.15 g, 3.10 mmol) was dissolved in THF (15 ml). Added H2O (15 ml) and sufficient THF to give a clear solution. A small crystal of cobalt chloride was added, followed by 2,2′-bipyridine (109 mg, 0.70 mmol). NaBH4 was added in portions until the blue color persisted. The color gradually faded, but was regenerated repeatedly by small additions of borohydride and HOAc. When HPLC indicated that the reaction was complete the reaction mixture was partitioned between EtOAc and H2O. HOAc was added until the pH of the aqueous phase was ca. 6, and then the aqueous phase was extracted with EtOAc. The combined organic phases were washed with brine, dried (Na2SO4), filtered and evaporated in vacuo. The residue was chromatographed on a small silica gel column eluting with 20% EtOAc/DCM. Fractions containing product were combined and evaporated in vacuo to give 0.82 g (74%) of the title compound as a white solid. MS (ESI−) for C19H19NO5S m/z 372.0 (M−H)−.
