Thionyl Chloride → 2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)acetyl chloride

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A suspension of 2,5-dihydro-2,5-dioxopyrrol-1-ylacetic acid (821 mg) in thionyl chloride (15.9 ml) was heated under reflux for 0.5 hours and the excess thionyl chloride was removed under vacuum. The residue was evaporated twice with dry toluene to afford 2,5-dihydro-2,5-dioxopyrrol-1-ylacetyl chloride [(5) where m=1] as a colourless, readily hydrolysed liquid. (The compound has been prepared previously by a less convenient route5). The crude acid chloride was dissolved in dry ether (25 ml) and added dropwise to an ice-cold solution of the hydrazinecarboxylate [(4) where n=1, 1.30 g] and triethylamine (588 mg) in dry ether (25 ml). The mixture was stirred in an ice bath for 1 hour then diluted with ethyl acetate and washed with water, dilute HCl, saturated NaHCO3 and brine, dried and evaporated. The residue was crystallised from ethyl acetate--petroleum ether to give the compound (6) as colourless plates (1.67 g; 82%) m.p. 157°-9° C. (Found: C, 53.1; H, 6.7; N, 10.8. C17H25N3O7 requires C, 53.25; H, 6.6; N, 11.0%).

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