Dehydration of 3- and 4-aryl- substituted 3-hydroxy acids in acetic anhydride in presence of zinc chloride

Abstract

The reaction of several di- and triaryl-substituted 3-aryl-3-hydroxy acids and a 4-aryl-3-hydroxy acid in acetic anhydride in the presence of anhydrous zinc chloride has been investigated. It has been shown that the reaction discovered with 3-(2′-thienyl)-substituted 3-hydroxy acids, namely, their conversion under the above stated conditions into α, β-unsaturated methyl ketones, 1,2 occurs also with 3-aryl 3-hydroxy acids but to a smaller degree due to the concurrent cyclization reaction which leads to indene-1-ones. It has been established that the unsaturated methyl-ketones obtained, containing three aromatic substituents at the CC bond, exist in s- cis-(CC, CO)-conformation. It has been found that with the 4-aryl-substituted 3-hydroxy acid almost no unsaturated ketone is obtained, whereas instead the main product is a 2,3-disubstituted 1-naphthol which is acetylated under the conditions of the reaction. Its structure has been proved by its UV, IR and NMR spectra and confirmed by the mass spectrum of the compound.