A study of some substituted cyclopentenes.

2-Methylcyclopent-2-ene-4-one 1-carboxylic acid monohydrate has been prepared by acidic hydrolysis of methyl 3-hydroxy-5-methylcyclopentadiene 1:2:4-tricarboxylate and of methyl 3-amino-5-methylcyclopentadiene 1:2:4-tricarboxylate. Alkaline decarboxylation of 2-methylcyeclopent-2-ene-4-one 1-carboxylic acid monohydrate has been shown to give 3-methyIcyclopent-2-ene-1-one which has also been synthesised by the cyclisation of acetonylacetone. The sodio derivative of methyl 3-hydroxy-5-methyl -cyclopentadiene 1:2:4-tricarboxylate has been prepared from methyl malonate and methyl alphaalpha'-dibromo-B-methylglutarate and has been converted, by treatment with ethyl iodide, into methyl 2-e thyl-3-hydroxy-5-methyIcyclopentadiene 1:2:4-tricarboxylate. The ethylated compound, on acidic hydrolysis, has been shown to give both 2-ethyl-4-methylcyclopent-4-ene-1-one and 2-ethyl-5-methylcyelopent-5-ene-3-one 1-carboxylic acid. The product of ozonolysis and subsequent oxidative hydrolysis, of 2-ethyl-4-methylcyclopent-4-ene-1-one has been characterised as alpha-ethyl-laevulic acid thus confirming the relative positions of the ethyl and methyl groups in the cyclic ketone. From the treatment of ethyl 3-methyleycloprop-2-ene 1:2-dicarboxylate with ethyl cyanoacetate was obtained the sodio derivative of ethyl 3-amino-5-methylcyclopentadiene 1:2:4-tricarboxylate. This has been shown, after treatment with ethyl iodide, to give ethyl 2-ethyl-3-imino-5-methylcyclopent-4-ene 1:2:4-tricarboxylate which after acidic hydrolysis gave 2- ethyl-5 -methylcyclopent-4-ene-3-one 1-carboxylic acid. This acid has been shown to differ from its isomer, 2-ethyl-5-mithylcyclopent-5-ene-3-one 1-carboxylic acid, by examination of the infra-red and ultra-violet absorption spectra, and from a study of the derivatives, of the two compounds. Alkaline decarboxylation of 2-ethyI-5-methyleyelopent-4-ene-3-one 1-carboxylic acid has been found to give a ketone which is identical with the previously mentioned 2-ethyl-4--methyIcyclopent-4-ene-1-one. Treatment of the sodio derivative of methyl 3-hydroxy-5-methyleyelopentadiene 1:2:4-tricarboxylate, with methyl iodide, gave a methylated product which, after acidic hydrolysis, has been shown to give 2:4-dimethylcyclopent-4-ene-1-one. This is regarded as further evidence of the position of entry of alkyl groups into the sodio derivative. A tentative structure has been suggested for an ethyl-methylcyclopentenone obtained after the acidic hydrolysis of the product of the reaction of ethyl 3-methylcycloprop-2-ene 1:2-1:2-dicarboxylate and ethyl alpha-cyanobutyrate. The assumption of a bridged ring in the sodio derivatives of methyl 3-hydroxy-5-methylcyclopentadiene 1:2:4-tricarboxylate and ethyl 3-amino-5-methylcyclopentadiene 1:2:4-tricarboxylate has been shown to be unnecessary