A. 3-Cyclopentene-1,1-dicarboxylic acid. A dry,
1-L, two-necked, round-bottomed flask (Note
1), equipped with a
Teflon-covered magnetic stirring bar, is charged under a current of
nitrogen with
33.0 g (0.250 mol) of dimethyl malonate,
50 mL of dry N,N'-dimethylpropyleneurea, DMPU, and
450 mL of dry tetrahydrofuran, THF (Note
2). The resulting solution is cooled by means of an
ice bath and treated with
5.00 g (0.629 mol) of lithium hydride powder in one portion (Note
3). The
nitrogen flow is discontinued, and the flask is capped with rubber septa and connected to a
Nujol-filled bubbler by means of a syringe needle. After 15 min, the cooling bath is removed and stirring is continued until
hydrogen evolution is complete (ca. 2 hr), whereupon
28.4 mL (0.269 mol) of cis-1,4-dichloro-2-butene (Note
4) is rapidly added by syringe. The mixture is heated by means of an
oil bath at 40-45°C for 24 hr (Note
5). After the mixture is cooled to 20°C, 50 mL of water is added dropwise followed by
31.5 g (0.750 mol) of solid lithium hydroxide monohydrate. After the reaction mixture is stirred at 20°C for an additional 24 hr, it is treated with 350 mL of water, stirred for 10 min, and then transferred to a
2-L separatory funnel. Neutral material is removed by extraction with five
500-mL portions of ethyl acetate, each of which is back-washed with
30 mL of aqueous saturated sodium chloride solution. The combined aqueous phases are then acidified with
160 mL of 6 N hydrochloric acid, and extracted three times with
500-mL portions of ethyl acetate. The
ethyl acetate extracts are combined, washed three times with
100 mL of 3 N hydrochloric acid and twice with
50 mL of aqueous saturated sodium chloride solution, dried over
sodium sulfate, filtered, and concentrated by rotary evaporation. After removal of traces of solvent under high vacuum (1 hr at 0.1 mm),
35.8 g (
92%) of
3-cyclopentene-1,1-dicarboxylic acid is obtained as an off-white solid, mp
163-165°C (Note
6).