Lithium Hydroxide → N-Propargylphenylalanine tert-butyl ester

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A solution of LiOH (400 mg, 16.7 mmol, 2.15 eq) in dry DMF (44 mL) containing activated 4 Å molecular sieves was stirred vigorously for 20 min, treated with Phe-Ot-Bu*HCl (2 g, 7.76 mmol, 1 eq), stirred for 45 min, treated with a solution 80% propargyl bromide (1.4 mL, 9.4 mmol, 1.21 eq) in toluene, stirred for 16 h and filtered through a pad of Celite™, which was washed with EtOAc (Cho, J. H. and B. M. Kim, Tetrahedron Lett. 2002, 43 1273-1276). The filtrate was washed three times with water, dried over MgSO4 and the volatiles were evaporated to provide an oil, which was purified by chromatography on silica gel using 30% EtOAc in hexane as eluent. Evaporation of the collected fractions gave ester 41 as yellow oil (1.66 g, 83%): Rf=0.53 (8:2 hexane/EtOAc); 1H NMR (400 MHz, CDCl3) δ 7.32-7.28 (m, 2H), 7.24 (m, 3H), 3.62 (t, J=6.9 Hz, 1H), 3.47-3.36 (m, 2H), 2.96 (m, 2H), 2.20 (m, 1H), 1.77 (s, 1H), 1.39 (s, 9H); 13C NMR (300 MHz, CDCl3) δ 172.9, 137, 129.2, 128.1, 126.4, 81.3, 81.0, 71.6, 61.5, 39.4, 36.5, 27.8. IR (thin film) v 3297, 2981, 2942, 1723, 1370, 1152, 700 cm−1; HRMS (LC-ESI) m/z calcd for C16H22NO2 [MH]+ 260.1645. Found 260.1634.

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