Synthesis of thieno-fused heterocycles through reiterative iodocyclization

Iodocyclization of ethynyl methyl sulfides gives 3-iodo-2-thiomethyl heterocycles, setting up the synthesis of thieno-fused systems through a subsequent iteration of alkyne coupling and iodocylization. This approach can also be exploited in the synthesis of polyfused thiophenes. In developing this protocol it was necessary to address issues associated with unfavourable electronic bias and redox sensitivity in some substrates. The manner in which these have been addressed should prove useful elsewhere in iodocyclization chemisty.