Citric Acid → 2-(5-(t-Butoxycarbonylamino)-2-chloropyrid-4-yl)-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2-ol

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Reaction Steps

To a stirred, cooled (−50° C.) solution of 643 mg(2.8 mmol) of 5-(t-butoxycarbonylamino)-2-chloropyridine in 8 mL of anhydrous THF was added 4.7 mL(7.9 mmol) of t-BuLi in pentane over 3 min. The solution was stirred an additional 35 min. at −50° C. after which time 1 mL(large excess) of 4-cyclopropyl-1,1,1-trifluoro-3-butyn-2-one. The solution was stirred an additional 20 min., warming to ambient temperature. The reaction was poured into 10% aq. citric acid, and the mixture was extracted with 1:1 ether-ethyl acetate. The organic extract was washed with saturated aq. NaHCO3, then brine, dried (MgSO4), and concentrated under reduced pressure. Chromatography on silica gel(gradient elution with 6:1 then 3:1 hexanes-ethyl acetate) afforded, after removal of solvent, 620 mg(56%) of 2-(5-(t-butoxycarbonylamino)-2-chloropyrid-4-yl)-4-cyclopropyl-1,1,1-trifluoro-3-butyn-2-ol as an amorphous solid. Mass spec.(NH3—CI): 391((M+H)+, 100%); 291((M+H-t-Boc)+, 49%). 1H NMR(300 MHz, CDCl3) δ 9.08(br. s, 1H); 8.29(br. s, 1H); 7.59(s, 1H); 1.50(s, 9H); 1.37-1.43(m, 1H); 0.81-0.97(m, 4H).

Provenance & Evidence