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.