Selectivity and isotope effects in hydronation of a naked aryl anion.

An aryl anion is produced by rapid addition of iodide to the p-benzyne diradical formed by cycloaromatization of an enediyne. The aryl anion is then hydronated (protonated or deuteronated) to form 1-iodotetrahydronaphthalene. Hydrons can be incorporated not only from water but also from such weak acids as dimethyl sulfoxide and acetonitrile. The relative reactivity of each pair of hydron donors is evaluated from competition experiments. A low selectivity is observed and taken as evidence for a high basicity of the aryl anion. Moreover, the same relative reactivities are obtained with Bu4NI as with LiI; therefore the species that undergoes hydronation is not an aryllithium but a naked aryl anion. These studies thus characterize the reactivity of a naked aryl anion in solution and contrast it with the reactivity of an aryllithium or an aryl Grignard.