Compound 31

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Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.

Step 1. To a mixture of 3-(3-(hex-5-yn-1-yl)-3H-diazirin-3-yl)propan-1-ol (30) (177 mg, 0.98 mmol) in DCM (5.0 mL) at 0 ^oC was added toluenesulfonyl chloride (206 mg, 1.08 mmol), triethylamine (330 μL, 1.96 mmol) and 4-(N,N-dimethylamino)pyridine (5 mg, 0.04 mmol). The mixture was stirred for 2 h, quenched with NH₄Cl (saturated), extracted with ethyl acetate, dried with sodium sulfate, filtered and concentrated under reduced pressure. The residue was chromatographed using 20 % ethyl acetate/cyclohexane to afforded 3-(3-(hex-5-yn-1-yl)-3H-diazirin-3-yl)propyl 4-methylbenzenesulfonate (126.1 mg, 0.38 mmol, 38%) as a colourless oil. ¹H-NMR (300 MHz, CDCl₃): δ 1.33 (m, 2H), 1.34 (m, 2H), 1.41 (m, 6H), 1.93 (t, J = 2.6 Hz, 1H), 2.11 (td, J = 7, 2.6 Hz, 2H), 2.45 (s, 3H), 3.94 (m, 2H), 7.33 (d, J = 8 Hz, 2H), 7.76 (d, J = 8 Hz, 2H). LCMS (ES+), m/z = 335.4 [M+H]⁺. Step 2. To a mixture of 3-(3-(hex-5-yn-1-yl)-3H-diazirin-3-yl)propyl 4-methylbenzenesulfonate (126.1 mg, 0.38 mmol) in absolute ethanol (4 mL) was added thiourea (30 mg, 0.40 mmol), the mixture was refluxed under N₂ for 16 h. Then sodium hydroxide (45 mg, 1.13 mmol) in EtOH:H₂O was added (0.5 mL of a 9:1 solution) and the refluxing was continued for 2 h. The reaction was concentrated water was added and the mixture was extracted with DCM. The organic fractions were dried, filtered and concentrated. The residue was chromatographed using 5 % ethyl acetate/cyclohexane to afforded 3-(3-(hex-5-yn-1-yl)-3H-diazirin-3-yl)propane-1-thiol (31) (29.5 mg, 0.15 mmol, 40%) as a colourless oil. ¹H-NMR (300 MHz, CDCl₃): δ 1.49 (m, 4H), 1.51 (m, 4H), 1.55 (m, 4H), 1.93 (t, J = 2.6 Hz, 1H), 2.13 (m, 2H). LCMS (ES+), m/z = 197. 3 [M+H]⁺.