Synthesis of Bis(indolyl)methanes Using N-Heterocyclic Carbene Salt as 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.