4-Fluoro-α-(1-hydroxy-1-methylethyl)benzeneacetic acid → 3-Methyl-2-(p-fluorophenyl)crotonic acid

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반응 단계

90 g of polyphosphoric acid were placed in a 350 ml sulphonation flask. Then, it was treated dropwise with a solution of 10.0 g (47 mmol) of 2-(p-fluorophenyl)-3-hydroxy-3-methylbutyric acid in 70 ml of CH2CL2 at 20-25°. The viscous, yellow colored mixture was stirred for 2 hours, with the temperature rising to 35°. After hydrolysis with ice-water the mixture was left to stand overnight and then treated with ether. The organic phase was separated, washed 3 times with water, dried over MgSO4, filtered and the filtrate was concentrated. The residue was dissolved in CH2CL2 and the solution was treated with hexane and concentrated on a rotary evaporator until crystallization occurred. After standing at RT for 1 hour the crystals were filtered off under suction and washed with cold hexane. There were obtained 67 g (73%) of 2-(p-fluorophenyl)-3-methylcrotonic acid as a white powder.

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