Palladium-Catalyzed Migratory Insertion of Isocyanides into C(thiophene)-SMe Bonds: Access to Atom-Transfer Reactions

Pd-II-catalyzed CN-directed addition of isocyanides to C(sp(2))-SMe bonds of thiophenes (generated in situ) effectively recycles the SMe activating group into thioimidate products. The catalytic sequence includes selective C(sp(2))-SMe bond activation/migratory insertion of isocyanides into C(sp(2))-Pd-IV and subsequent C(sp(2))-SMe bond-forming reductive elimination from imidoyl-Pd-IV-SMe complexes. Through these transition-metal-catalyzed addition reactions we have established isocyanides as a new template for atom-transfer reactions. This groundbreaking research avoids the use of ancillary ligands that is a constant feature of all previously reported addition reactions with C-S bonds. This process proceeds through a high-valent Pd-II/IV catalytic cycle, which - to the best of our knowledge - has not been previously reported in this regard. Isocyanide insertion into C(Ar)-S bonds through addition is also unprecedented. Finally, the resulting thioimidates were demonstrated to be convenient precursors for the synthesis of thieno[2,3-c]pyrroles by targeting the recycled SMe group for the second time in a cascade reaction process.