Hydration Reactivity of Persistent Conjugated Ketenes

Article abstract of DOI:10.1021/jo00273a013

The acid, neutral, and base hydrations of the crowded alkenylketene 1 and the arylketenes i-PrCPh=C=O (2) and t-BuCPh=C=O (3) have been measured, together with solvent isotope effects and general acid catalysis of the hydration of 1.The arylketenes 2 and 3 are the first for which acid-catalyzed hydration has been demonstrated.These ketenes show significantly lower reactivity than simple ketenes, and this is interpreted as the result of both steric and electronic factors operating in mechanisms involving rate-limiting proton transfer to carbon (the γ-carbon in 1) for the acid-catalyzed reaction, while both the neutral and hydroxide-induced reactions involve rate-limiting nucleophilic attack in the plane of the ketene on the carbonyl carbon.