Syntheses of 3-(2,4-dimethyl-5-oxocyclopent-1-enyl)propionic acid and 2-methyl-3-oxo-4-isopropylidenecyclopentanecarboxylic acid

Abstract

2-Methyl-2-prop-2-ynylcyclohexane-1,3-dione (8), prepared by alkylation of the potassium salt of 2-methylcyclohexane-1,3-dione (7) with prop-2-ynyl bromide in dimethylformamide, gave 2-acetonyl-2-methylcyclohexane-1,3-dione (1) on treatment with mercurated Amberlite IR 120 resin in methanol. An attempt to achieve the same result by use of boron trifluoride-ether complex and red mercury(II) oxide in methanol gave methyl 4-(3,5-dimethyl-2-furyl)butyrate (9). Attempts to cyclodehydrate compound (1) with aqueous 5% potassium hydroxide or potassium t-butoxide furnished an isomeric acid which spectral data indicated could be either 3-(2,4-dimethyl-5-oxocyclopent-1-enylpropionic acid (2) or 2-methyl-4-isopropylidene-3-oxocyclopentane-carboxylic acid (4). Both these acids were synthesised independently and the product of alkali cleavage was shown to be compound (2).