Mechanistic Insights into Nickel-Catalyzed Cycloisomerizations

A nickel-catalyzed cycloisomerization coupling an allylic alcohol with an alkyne has been developed Mechanistic insights gained through deuterium-labeling crossover studies and stereochemical probes illustrate that oxidation of the allylic alcohol to a metal-free enone is not involved in the cyclization pathway. The intermediacy of a metallacycle directly derived from oxidative cyclization of Ni(O) with the allylic alcohol and alkyne is consistent with the results obtained. The simple mechanistic probes employed could be useful in the study of many classes of cycloisomerization processes.