Reaction Steps
To a solution of N′-((2R,3S)-2-(3-chloro-4-cyano-2-methylphenylamino)-3-hydroxybutanoyl)-4-(trifluoromethyl)benzohydrazide (1.0 g, 2.20 mmol) in anhydrous THF (90 mL) at room temperature was added 2-tert-butylamino-2-diethylamino-1,3-dimethyl perhydro-1,3,2-diazaphosphorine on polystyrene (2.2 mmol base/g) (3.0 g, 6.60 mmol) followed by para-toluenesulfonyl chloride (419 mg, 2.20 mmol) and the mixture was stirred for one hour. The mixture was filtered under suction and the residue washed with acetone (2×100 mL) followed by Methanol (2×150 mL). The filtrate was concentrated under reduced pressure to provide a yellow oil, which was purified by flash chromatography over silica gel (20-40% EtOAc in hexanes) to provided (Z)-2-chloro-3-methyl-4-(1-(5-(4-(trifluoromethyl)phenyl)-1,3,4-oxadiazol-2-yl)prop-1-enylamino)benzonitrile, the less polar component as a colourless solid (122 mg, 13%) and 2-chloro-4-((1R,2S)-2-hydroxy-1-(5-(4-(trifluoromethyl)phenyl)-1,3,4-oxadiazol-2-yl)propylamino)-3-methylbenzonitrile, the more polar component as a yellow oil (336 mg, 35%): Less polar compound; 1H NMR (400 MHz, d6-acetone, δ in ppm) 8.27 (d, J=8.0 Hz, 2H), 7.93 (d, J=8.0 Hz, 2H), 7.44 (d, J=8.6 Hz, 1H), 7.13 (br s, 1H), 7.04 (q, J=7.2 Hz, 1H), 6.62 (d, J=8.8 Hz, 1H), 2.47 (s, 3H), 1.91 (d, J=7.0 Hz, 3H): More polar compound; 1H NMR (400 MHz, d6-acetone, δ in ppm) 8.22 (d, J=8.0 Hz, 2H), 7.92 (d, J=8.2 Hz, 2H), 7.48 (d, J=8.6 Hz, 1H), 6.87 (d, J=8.8 Hz, 1H), 5.70 (d, J=8.6 Hz, 1H), 5.16 (dd, J=3.5, 8.6 Hz, 1H), 4.86 (br d, J=4.3 Hz, 1H), 4.70-4.61 (m, 1H), 2.40 (s, 3H), 1.43 (d, J=6.4 Hz, 3H).
