Acetylenic Acids. IV. The Reactions of Alkoxy-Substituted Phenylpropiolic Acids and Esters with Sulfur Halides, Particularly Thionyl Chloride

Abstract

3,4-Dialkoxy-substituted phenylpropiolic acids and esters react with thionyl chloride to give good yields of substituted 1-benzothiophen systems. Similar reactions of m-and p-methoxyphenylpropiolic acids and 3,4,5-trimethoxyphenylpropiolic acid, which yield mixtures of products, are reported. In contrast, 2,5- and 2,3-dimethoxyphenylpropiolic acids gave mixtures in which a coumarin is the major product. The effect of adding pyridine to the reaction mixture is outlined. Reactions involving sulfur monochloride and sulfur dichloride generally gave much lower yields of these products. Attempts to form organometallic intermediates from the 3-chloro-1-benzothiophen products were unsuccessful.