Lawesson's reagent → 5-(Tert-butoxycarbonylamino-methyl)-[1,3,4]thiadiazole-2-carboxylic acid ethyl ester

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To the solution of ethyl 2-(2-(2-(tert-butoxycarbonylamino)acetyl) hydrazinyl)-2-oxoacetate (9-4) (228 mg, 0.6913 mmol) in THF (10 mL) was added lawesson's reagent (354 mg, 0.8669 mmol). The solution was heated to reflux for 3 h. Then solvent was evaporated under reduced pressure and the residue was purified by chromatography on silica gel with the eluant (PE/EA/NEt3=10/1/1%; 5/1/1%; 2/1/1%). The yellow solid was obtained as the product (520 mg, 69%). 1H NMR (500 MHz, CDCl3) δ 5.31 (br, 1H), 4.76 (d, J=6.1 Hz, 2H), 4.51 (d, J=14, 7.1 Hz, 2H), 1.60-1.39 (m, 12H); LRMS (ESI) calculated M+H for C11H18N3O4S: 288.3; Found: 288.1.

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