Boron Trichloride → 4-Chloro-7-(2-C-ethyl-beta-D-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine

To a solution of the compound from Step B (307 mg, 0.45 mmol) in dichloromethane (8 mL) was added boron trichloride (1M in dichloromethane) (4.50 mL, 4.50 mmol) at −78° C. The mixture was stirred at −78° C. for 1 h, then at −10° C. for 3 h. The reaction was quenched by addition of methanol/dichloromethane (1:1) (10 mL), stirred at −15° C. for 30 min, and neutralized by addition of aqueous ammonium hydroxide. The mixture was evaporated in vacuo and the resulting oil purified on silica gel using methanol/dichloromethane (1:9) as eluent. Fractions containing the product were pooled and evaporated in vacuo to give the desired product (112 mg) as a colorless foam.