Reaction Steps
To a 25 mL flame dried flask with stir bar cooled to room temperature was added alkyne 20 (0.115 g, 0.46 mmol) dissolved in anhydrous CH2Cl2. The reactant was cooled to 0° C. and chlorosulfonyl isocyanate (0.08 mL, 0.92 mmol) was added dropwise. After 15 min, the reaction mixture was brought to room temperature and followed by TLC. The reaction was quenched with water and extracted with ether. The organic extracts were washed with brine, dried over MgSO4, and filtered. The filtrate was concentrated and purified by flash column chromatography (SiO2, 7 g, 25% EtOAc/hexanes) to give the terminal acetylene 23 as a white solid (0.092 g, 68% yield): TLC Rf=0.1 (25% EtOAc/hexanes); mp 113.6-115.3° C.; 1H NMR (500 MHz, CDCl3) δ 7.61 (d, J=7.8 Hz, 1H), 7.56 (d, J=8.5 Hz, 2H), 7.19 (d, J=8.5 Hz, 2H), 7.15 (dd, J=7.8, 1.4 Hz, 1H), 7.01 (d, J=1.7 Hz, 1H), 4.21 (qd, J=7.0, 2.3 Hz, 1H), 3.88 (s, 3H), 2.23 (d, J=2.4 Hz, 1H), 1.47 (d, J=7.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 189.2, 156.4, 155.6, 150.3, 140.6, 138.9, 133.1, 130.3, 128.3, 128.2, 122.1, 119.7, 109.6, 87.7, 69.6, 60.6, 55.7, 25.3, 22.8, 21.2, 14.4; IR (neat cm−1) 3423, 3308, 3268, 3199, 2969, 2341, 2105, 1698, 1606, 1494, 1378, 1213, 586; HRMS (DART, M++H) m/z 296.1300 (calculated for C18H18NO3, 296.1287).
