Abstract: A new method has been developed for the Pd-catalyzed direct carbonylation of indoles with phenylacetylenes. The process involved the initial iodination of the indole to afford the corresponding 3-iodo-indole, which was subsequently carbonylated with a variety of different alkynes using Pd(0) to yield the indole-3-alkynones. In contrast to the traditional Pd-catalyzed oxidative carbonylation strategy, which involves the Pd(II)-mediated activation of the aromatic C–H bonds, the aromatic C–H bonds in the current process were activated by iodine oxidation, eliminating the problems associated with the reduction of Pd(II) to Pd(0) under the CO atmosphere. Following an extensive screening process, Pd(OAc)₂/CuI was identified as the most efficient catalyst system for the reaction in the presence of a base and iodine as an oxidant under mild conditions (0.2 MPa CO, 90 ^oC). The reaction provided the desired products in moderate to excellent isolated yields (up to 94%) and good tolerance to a variety of different functional groups. The structure of a representative alkynone product (3he) was unambiguously verified by X-ray single crystal structure analysis. Furthermore, the carbonylation products underwent a three-component reaction with sodium azide and benzyl bromide to give the corresponding 1,2,3-triazole analogues in the absence of any catalyst, thus expanding the synthetic application of the current methodology.

Key words: Carbonylation, Carbon monoxide, Palladium, Indole-3-alkynone, Triazole