Concept

Nicholas reaction

Résumé
The Nicholas reaction is an organic reaction where a dicobalt octacarbonyl-stabilized propargylic cation is reacted with a nucleophile. Oxidative demetallation gives the desired alkylated alkyne. It is named after Kenneth M. Nicholas. Several reviews have been published. Reaction mechanism The addition of dicobalt octacarbonyl to a propargylic ether (1) gives the dicobalt intermediate 2. Reaction with HBF4 or Lewis acid gives the key dicobalt octacarbonyl-stabilized propargylic cation (3a and 3b). Addition of a nucleophile followed by a mild oxidation gives the desired substituted alkyne (5). The likely intermediates in the reactions, [(propargylium)Co2(CO)6]+ cation 3, possessed considerable stability. It was, in fact, possible to observe these cations by 1H NMR at 10 °C when generated using d-trifluoroacetic acid. Later, Richard E. Connor and Nicholas were able to isolate salts of such cations 3 as stable, dark red solids by treat
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