Abstract
Examination of the base-catalysed condensation of ethyl chloroacetate with indan-1-one has established that potassium t-butoxide is preferable to either sodamide or sodium ethoxide as condensing agent. Hydrolysis of the ester formed is shown to yield not the expected glycidic acid (indan-1-spiro-2'-oxiran-3'-carboxylic acid), but the isomeric alpha-hydroxyindenyl-1(3)-acetic acid together with a small proportion of indenylidene-1-acetic acid. The structure assigned to the hydroxy acid is based upon spectroscopic data, the chemical properties of the ester and of the acid, and upon its identity with the acid formed by Claisen hydrolysis of authentic ethyl alpha-hydroxy- indenyl-1(3)-acetate. Decarboxylation of the acid, which occurs at the melting-point, is accompanied by an unusual isomerisation to yield 1-formylindane, the expected decarboxylation product of the glyoidic acid. Although it is found that some indenylidene-acetic acid is formed as a by-product in the Claisen hydrolysis, this does not rule out other precursors of the acid being formed in the condensation reaction e.g. by reaction involving the active methylene group of the enolised ketone. This aspect was investigated by the use of substituted indan-l-ones which would yield different products by the alternative paths. The product from 5-methoxyindan-1-one is shown to be 5-methoxyindenylidene-l-acetic acid, proving that condensation with the chloroester occurs with the carbonyl group of the ketone, a result confirmed by the corresponding reaction with 6-methoxyindan-1-one, With 2,2-dimethylindan-1-one, a corresponding dienoic acid cannot be formed. The condensation with ethyl chloroacetate occurs less readily than with indan-1-one to give an ester (contaminated with the alpha-oxoester), which on hydrolysis gives a very low yield of a product best formulated as the glycidic acid. The condensation is accompanied by the formation of ethyl ethoxyacetate derived from ethyl chloroacetate by interaction with the condensing agent. Phenyl 2-phenylethyl ketone, the open-chain analogue of indan-1-one, yields the normal glycidic ester in this reaction; no rearrangement products were isolated. Decarboxylation of the acid (to yield 2,4-diphenylbutan-1-al) occurs more readily than with the aforementioned hydroxy-acid.