Silver(I)-Catalyzed Addition of Phenols to Alkyne Cobalt Cluster Stabilized Carbocations

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A smooth catalytic method to use phenols as the nucleophilic partner in the Nicholas reaction has been developed. The method uses either AgIor AuIcatalysts with AgClO4or AgBF4as the most efficient catalysts tested. Neither additional additives nor cocatalysts were required and the formation of the corresponding phenol adducts occurred in excellent yields. The process has the single limitation of the inability of less nucleophilic phenols (4-nitrophenol) to generate the corresponding adducts. Additionally, the reaction is highly diastereoselective. DFT calculations allow a catalytic cycle to be proposed that involves trimetallic intermediates; the rate-determining step of the reaction is hydroxy-group elimination in a cobalt–silver trimetallic intermediate.