4-Methoxy-2,2,6,6-tetramethylpiperidinyl-1-oxy → 1-(5,6-dichloro-1H-benzoimidazol-2-yl)-2,2,2-trifluoro-ethanone

Participants

Reaction Conditions

Reaction Steps

A 3-L 4-neck flask equipped with a thermocouple controller, an overhead mechanical stirrer, an addition funnel, and a nitrogen inlet/outlet adaptor was charged with 1-(5,6-dichloro-1H-benzoimidazol-2-yl)-2,2,2-trifluoro-ethanol (91.0 g, 0.32 mol), 4-methoxy-TEMPO (14.3 g, 0.077 mol), and KBr (4 g, 0.0336 mol) in THF (900 mL). The brown homogenous solution was stirred for 15 min while cooling to −10° C. After cooling, NaOCl (670 ml) was added dropwise over a ½ h period. The reaction mixture was diluted with EtOAc (1.5 L) and H2O (1.5 L). When the effervescence ceased, the phases were split and the aqueous layer was back extracted with EtOAc (2 L). The combined organic layer was washed with brine (2 L); dried over Na2SO4, filtered and evaporated to dryness to yield a crude residue. The crude residue was purified by flash chromatography using SiO2 (1 kg) and 40% EtOAc/hexanes (24 L) and the product dried in vacuo for 18 h at 50° C. to yield 1-(5,6-dichloro-1H-benzoimidazol-2-yl)-2,2,2-trifluoro-ethanone as a yellow solid.

Provenance & Evidence