A solution of 280 mg (1.26 mmol) of 4,4-dimethyl-6-carboxythiochroman and 252 mg (2.52 mmol) of triethylamine in 15 ml of chloroform was stirred at room temperature for 0.5 hours and then treated with 481 mg (1.26 mmol) of bis(2-oxo-3-oxazolidinyl)phosphinic chloride. The reaction mixture was stirred for 0.5h, treated with 209 mg (1.26 mmol) of ethyl 4-hydroxybenzoate and then stirred at room temperature for a further 12 hours. The reaction mixture was washed successively with dilute HCl and saturated sodium bicarbonate solutions The organic layer was concentrated in-vacuo and the resultant crude product purified by flash chromatography (silica; 10% ethyl acetate in hexane) followed by reversed-phase high pressure liquid chromatography (Whatman Partisil M20 10/50 ODS-2; 10% water in acetonitrile) to give the title compound as a colorless oil.
