Synthetic Routes to N‐Heterocyclic Carbene Complexes: Pyridine–Carbene Tautomerizations

70 years ago the existence of the 2-carbene isomer of pyridine, which arises by pyridine–carbene tautomerization (see scheme), was postulated. Now it has been prepared from pyridine as a stable carbene complex by metal-induced CH activation. This pyridine–carbene tautomerization is described and discussed along with other analogous carbene tautomerization reactions.