Efficient synthetic approach to substituted benzo[b]furans and benzo[b]thiophenes by iodine-promoted cyclization of enaminones

An efficient synthetic approach to the substituted benzo[b]furan and benzo[b]thiophene scaffolds by iodine-mediated cyclization of the corresponding enaminones is described. This protocol was applied to a large series of these latter precursors to afford the respective benzoheterocycles substituted at the C-2 position by a carbonyl group functionality. A study of the factors that control this process reveals that the reactivity depends on the presence of electron-donor groups in the aryl ring of the aryloxycarbonylic and arylthiocarbonylic moieties.