Institute of Crystallography - CNR

Synthesis of benzothienofuranones and dihydrobenzothienopyranones by palladium iodide-catalyzed carbonylative double cyclization

3-(2-(Methylthio)phenyl)prop-2-yn-1-ols have been successfully converted in one synthetic step into benzo[4,5]thieno[2,3-c]furan-1-ones by a PdI2/KI-catalyzed oxidative carbonylative double cyclization process, performed in MeCN under relative mild conditions (1-10 mol % PdI2, 7 equiv of KI, 80 °C, 60 atm of a 4:1 mixture CO-air). The process takes place through an ordered sequence of steps, involving 5-endo-dig S-cyclization, iodide-promoted demethylation of the ensuing sulfonium salt, CO insertion, a second cyclization (possibly, through the formation of a palladacycle intermediate followed by reductive elimination), and Pd(0) reoxidation by oxygen (from air) used as external benign oxidant. Under similar conditions, 4-(2-(methylthio)phenyl)but-3-yn-1-ols, bearing a butynol moiety ortho to the methylthio group, led to a mixture of double cyclization and dicarbonylation products, however, by slightly tuning the reaction conditions, dihydrobenzo[4,5]thieno[3,2-c]pyran-1-ones could be selectively obtained with no formation of the dicarbonylated byproduct. The structures of four representative products, including two tetracyclic derivatives, have been confirmed by XRD analysis.

Journal of catalysis (Online)
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Ida Ziccarelli, Raffaella Mancuso, Domenico Santandrea, Angela Altomare, Diego Olivieri, Carla Carfagna, Bartolo Gabriele
Authors IC CNR