Synthesis of bis(indolyl)methanes using N-heterocyclic carbene salt as a C1 precursor

We herein describe an alkylation reaction of indoles with NHC salts to access bis(indolyl)methanes as product. The NHC salt (or free NHC) serves as a C1 precursor due to decomposition of its N-heterocyclic ring. Although the exact roles of zinc powder and acetic/formic acid remain elusive, both of them are indispensable for this reaction. Two possible reaction pathways are proposed based on the results of mechanistic experiments. We describe an alkylation reaction of indoles with N-heterocyclic carbene (NHC) salts to access bis(indolyl)methanes where the NHC salt serves as a C1 precursor.