Synthesis of Thio-lignan Analogues, Bioequivalent Salvinal without Unfavored Aldehyde

Synthesis of Benzothiophene-3-carboxylic Esters by Palladium Iodide-Catalyzed Oxidative Cyclization-Deprotection-Alkoxycarbonylation Sequence under Aerobic Conditions

A palladium-catalyzed carbonylative approach to benzothiophene-3-carboxylic esters, starting from simple and readily available building blocks [2-(methylthio)phenylacetylenes, CO, an alcohol, and O₂ (from air)], is reported. The process is catalyzed by the simple PdI₂/KI catalytic system to give the desired products in fair to high yields (57-83%). Interestingly, the reaction also works nicely in the ionic liquid BmimBF₄ as the solvent, with the possibility to recycle the catalytic system several times without appreciable loss of activity.