was treated carefully with a 2 m hcl solution until the precipitation dissolved almost completely ph 2 0 the reaction mixture was stirred over night at room temperature the reaction mixture was then treated with a 1m versenol solution until the suspension became clear subsequently it was diluted to 2000 ml the ph adjusted to 7 5 and the solution applied to an ion exchange chromatography column the fractions containing the product were pooled and the product was isolated as triethylammonium salt 136 mg 0 11 mmol 4 which was used in the next step without further purification ms es m z 824 m h u2212 to a solution of 1 2 3 5 tetra o acetyl u03b2 d ribofuranose 9 g 28 mmol in 120 ml of dichloromethane at u2212 78 u00b0 c was added dropwise 3 52 ml of boron trifluoride diethyl etherate 28 mmol 1 equiv the resulting mixture was stirred at u2212 78 u00b0 c for 30 min and 3 48 g of 4 methoxyphenol 28 mmol 1 equiv was added the mixture was slowly warmed to rt and stirred overnight 300 ml of saturated sodium bicarbonate solution was added the organic layer was separated the water layer was extracted with dichloromethane twice 250 ml the combined organic layer was washed with brine and dried over sodium sulfate the solvents were removed under reduced pressure and the crude material was recrystallization from hexanes ethyl acetate 30 to afford 6 9 g of u03b2 isomer product.