3-Cyclopentene-1,1-dicarboxylic acid

B. 3-Cyclopentene-1 -carboxylic acid. A 250-mL, one-necked, round-bottomed flask is charged with 35.8 g of 3-cyclopentene-1,1-dicarboxylic acid and then fitted with a reflux condenser capped with a rubber septum and connected to a Nujol-filled bubbler by means of a syringe needle. The contents of the flask are heated in an oil bath at 170-175°C until carbon dioxide evolution is complete (ca. 2 hr) and then allowed to cool to room temperature. The resulting oil is transferred to a 50-mL flask and vacuum distilled without fractionation to provide 23.0 g (89% or 82% overall from dimethyl malonate) of 3-cyclopentene-1-carboxylic acid as a clear, colorless oil, bp 88°C (2 mm) (Note 7). 

CYCLOPENTENE-1-CARBOXYLIC ACID (7686-77-3), 75, 195 3-Cyclopentene-1,1-dicarboxylic acid (88326-51-6), 75, 195 Cyclopropanations, enantioselective, 76, 97... 

Synonyms Chrysanthemum dicarboxylic acid monomethyl ester pyrethrolone Chrysanthemum dicarboxylic acid monomethyl ester pyrethrolone ester Cyclopropaneacrylic acid, 3-carboxy-a,2,2-trimethyl-, 1-methyl ester, ester with 4-hydroxy-3-methyl-2-(2,4-pentadienyl)-2-cyclopenten-1-one Pyrethrin Pyrethrolone, chrysanthemum dicarboxylic acid methyl ester ester... 

Scheme 7. RCM of diethyl-diallyl-malonate to give the diethyl ester of 3-cyclopentene-l,l-dicarboxylic acid.

CaHioBr20a, cis-1,2-Dibromo-1,2-dicarbomethoxycyclobutane, 31B, 85 CaHioBr20ft, trans-1,2-Dibromo-l,2-dicarbomethoxycyclobutane, 31B, 85 CaHio02r Dicyclopropylethanedione, 42B, 100 CaHiiN, 6-(N,N-Dimethylamino)pentafulvene, 40B, 133 CaHiiNOa, Cyclopentene-1,2-dicarboxylic acid N-methyl-half-amide, 39B, 92... 

The preparation described here of 3-cyclopentene-1-carboxylic acid from dimethyl malonate and cis-1,4-dichloro-2-butene is an optimized version of a method reported earlier3 for obtaining this often used and versatile building block.6 The procedure is simple and efficient and requires only standard laboratory equipment. 3-Cyclopentene-1-carboxylic acid has previously been prepared through reaction of diethyl malonate with cis-1,4-dichloro(or dibromo)-2-butene in the presence of ethanolic sodium ethoxide, followed by hydrolysis of the isolated diethyl 3-cyclopentene-1,1-dicarboxylate intermediate, fractional recrystallization of the resultant diacid to remove the unwanted vinylcyclopropyl isomer, and finally decarboxylation.2>7 Alternatively, this compound can be obtained from the vinylcyclopropyl isomer (prepared from diethyl malonate and trans-1,4-dichloro-2-butene)8 or from cyclopentadiene9 or cyclopentene.10 In comparison with the present procedure, however, all these methods suffer from poor selectivity, low yields, length, or need of special equipment or reagents, if not a combination of these drawbacks. 

The last synthesis to evolve which is due to Ito and his coworkers is interesting in that it relies on a stereospecific skeletal rearrangement of a bicyclo[2.2.2]octane system which in turn was prepared by Diels-Alder methodology (Scheme XLVIII) Heating of a toluene solution of cyclopentene 1,2-dicarboxylic anhydride and 4-methylcyclohexa-l,4-dienyl methyl ether in the presence of a catalytic quantity of p-toluenesulfonic acid afforded 589. Demethylation was followed by reduction and cyclization to sulfide 590. Desulfurization set the stage for peracid oxidation and arrival at 591. Chromatography of this intermediate on alumina induced isomerization to keto alcohol 592. Jones oxidation afforded diketone 593 which had earlier been transformed into gymnomitrol. 

Dimethyl carbonate Carbonic acid, dimethyl ester (616-38-6), 76, 170 Dimethyl 3-cyclopentene-1,1-dicarboxylate, 75, 197... 

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