SYNTHETIC STUDIES ON VITAMIN A

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Abstract
The condensation of a variety of aldehydes with methyl or ethyl senecioate by means of alkali amide to yield γ-alkylidene- or arylidene-β-methylcrotonic acids R-CH=CH-C(CH3)=CH-COOH is described. The ultraviolet absorption spectra of these and chemical behavior showed the arylidene compounds to have a cis relationship of the R and -C(CH3)=CH-COOH groups about the newly created double bond, when sodium amide was used as a condensing agent. If potassium amide was a condensing agent, the results were some-what complex. In the case when R was C6H5, 2, 4-di-trans-acid was obtained. When R was C6H5-CH=CH-, the same result was obtained as the case of sodamide, namely the product was 2-trans-4-cis-acid. When R was furyl, the 2-cis-4-trans-acid was the product. When R was alkyl and the condensing agent was potassium amide, the products seemed to be 2, 4-di-trans-acids as iodine and light failed to isomerize them.

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