Oxidant-Free Direct Coupling of Internal Alkynes and 2-Alkylpyridine via Double C-H Activations by Alkylhafnium Complexes

摘要

We have developed a novel oxidant-free direct cross-coupling reaction of 2,6-lutidine and internal alkynes leading to five-membered carbocyclic compounds mediated by nonmetallocene cationic hafnium alkyl complexes. Mechanistic studies of the coupling reaction showed that the reaction begins with C(sp~3)-H bond activation via δ-bond metathesis, after which the coordinatively unsaturated hafnium center mediates fuerther insertion, migration, and β-H elimination reactions to give five-membered carbo-cycles from readily available substrates.