alpha‐phenylpropionic acid derivatives. Synthesis and dethiation of 5‐benzoylbenzo[b]thiophene‐3‐carboxylic acid

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Abstract
The total synthesis of the title compound 8 started with p‐thiocresol which was acylated with oxalyl chloride to give compound 1. This product underwent a condensation reaction with chloroacetic acid under basic conditions yielding compound 2. Two different synthetic pathways were used to convert compound 2 into the title compound 8. The first consisted in decarboxylation of 2 to 3, which was then converted to the ester 4, which was brominated and the product 5 was subjected to a Friedel‐Craft's reaction with benzene. The resulting benzyl derivative 6 was oxidized to the benzoyl stage i.e. compound 7, which was finally hydrolyzed to 8. The second pathway was similar to the first one so that the steps of esterification, bromination, Friedel‐Craft's alkylation and oxidation started with the dicarboxylic acid 2. Thus compounds 12–16 were obtained, and the last product was decarboxylated to 8. The yields in both procedures were similar. Finally, the dethiation of compound 8 with Raney nickel afforded compounds 18, 19 and 20.

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