To a stirred mixture of 2-(2-hydroxy-4-nitrophenyl)benzothiazole (0.15 g, 0.55 mmol), triphenylphosphine (0.216 g, 0.825 mmol) and N,N-dimethylethanolamine (0.059 g, 0.66 mmol) in dry THF (10 ml) at 0° C. was added dropwise DIAD (0.167 g, 0.825 mmol). The reaction mixture was stirred at 0° C. for 0.5 h, then left to rise to room temperature overnight. The solvent was removed under reduced pressure and the residue was purified by flash chromatography (20:1 DCM/MeOH) to give the title compound (0.089 g, 47%) as a yellow solid.
