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

A smooth catalytic method to use phenols as the nucleophilic partner in the Nicholas reaction has been developed. The method uses either AgI or AuI catalysts with AgClO4 or AgBF4 as 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. Making the unreactive react: Phenols can be used as nucleophilic partners in the Nicholas reaction by using either silver(I) or gold(I) catalysts (see figure). Neither additional additives nor cocatalysts are required and the formation of the corresponding phenol adducts occurs in excellent yields. In contrast, the “classical” Nicholas reaction with phenols is not possible.