Hydrochloric Acid → tert-Butyl 1H-pyrrol-1-ylcarbamate

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A flask (fitted with a Dean-Stark trap) containing a stirred solution of tert-butylcarbazate (100, 0.757 mol), 2,5-dimethoxytetrahydrofuran (108 g, 0.832 mol) and 2 N HCl (10 mL) in 1,4-dioxane (700 mL) was heated under nitrogen at 90° C. As the reaction progressed over several hours, the solution changed from pale yellow to orange and began to reflux. The reaction was monitored by the amount of distillate collected in the D/S trap (primarily CH3OH, 2 moles/1 mole reagent). As methanol collection approached the theoretical amount (50 mL) a sample was analyzed by TLC (silica gel, 1:3 EtOAc/hexane, ninhydrin stain) to confirm reaction completion. Heating was shut off and the reaction was allowed to cool somewhat before adding saturated sodium bicarbonate solution (˜25 mL) to neutralize the hydrochloric acid. The quenched mixture was filtered through a sintered-glass funnel and concentrated in vacuo to leave an orange, semi-solid residue. The residue was suspended in diethyl ether (minimum volume) and the nearly colorless solids were collected by suction filtration, washed with hexane and air-dried to afford 60.2 g (40%) of product. A second crop (yellow-tan solids) from the mother liquors was isolated: 29.0 g, (19%). Additional material which was present in the mother liquors could be recovered by silica gel chromatography to increase the yield. 1H-NMR (CD3OD): δ 10.23 (br s, 1H), 6.66 (t, 2H, J=2.2 Hz), 5.94 (t, 2H, J=2.2), 1.42 (s, 9H); MS: GC/MS (+esi): m/z=182.9 [MH]+

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