Diethyl acetylenedicarboxylate → 3-[2-(1,1-Dioxo-1lambda6-[1,2]thiazinan-2-yl)-phenyl]-5-ethoxycarbonylmethyl-2-methyl-2,5-dihydro-[1,2,4]oxadiazole-5-carboxylic acid ethyl ester

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Reaction Steps

To a stirred solution of 2-(1,1-dioxo-1λ6-[1,2]thiazinan-2-yl)-N-hydroxy-N-methyl-benzamidine (3.5 g) in ethanol (100 mL, 200 proof) was added diethyl acetylene-dicarboxylate (3.2 mL, 20 mmol) and the resulting mixture stirred at room temperature for 30 min. The mixture was concentrated and purified on a silica gel column (10%–30% ethyl acetate/hexanes) to afford the title compound as a yellow oil (3.62 g, 40% yield). 1HNMR (300 MHz, CDCl3) δ: 7.57 (2H, td, J=7.14, 1.28 Hz,), 7.50 (1H, td, J=7.68, 1.83 Hz), 7.39 (1H, td, J=7.50, 1.46 Hz), 4.34–4.22 (2H, m), 4.18 (2H, q, J=7.08 Hz), 3.42 (1H, d, J=16.47 Hz), 3.22–3.18 (2H, m), 3.07 (3H, s), 3.05 (1H, d, J=16.46 Hz), 2.38–2.24 (2H, m), 2.00–1.42 (2H, m), 1.33 (3H, t, J=7.14 Hz), 1.26 (3H, t, J=7.14 Hz). HRMS calcd for C20H28SN3O7 (M+H): 454.1648; found: 454.1650.

Provenance & Evidence