Rui Lang

A General Method for Palladium-Catalyzed Direct Carbonylation of Indole with Alcohol and Phenol

A novel strategy involving a first oxidative iodination and subsequent Pd(0)-catalyzed carbonylation to yield indole-3-carboxylate has been developed. It showed perfect generality to indole, alcohol, and phenol. The current methodology could also be conveniently applied to the synthesis of biologically active tropisetron from simple indole and tropine.

pH-Responsive N-heterocyclic carbene copper(I) complexes: syntheses and recoverable applications in the carboxylation of arylboronic esters and benzoxazole with carbon dioxide

A pH-controlled monophasic/biphasic switchable system has been developed as a green and novel strategy for homogeneous catalyst recycling, which has been successfully applied to the Cu-NHC-catalyzed carboxylation of organoboronic esters and benzoxazole with carbon dioxide. Additionally, the present strategy could also be extended to the Ag-NHC-catalyzed carboxylation of terminal alkyne. The tertiary amine-functionalized catalysts could be used for at least four times with a slight loss of activity.

Four-Component Synthesis of β-Enaminone and Pyrazole through Phosphine-Free Palladium-Catalyzed Cascade Carbonylation

The carbonylative domino synthesis of enaminones and pyrazoles has been performed with the NN bidentate palladium catalyst to achieve excellent selectivity. These results have confirmed that the carbonylative Sonogashira coupling of iodobenzenes with terminal alkynes is accompanied by the Michael addition of amines or phenylhydrazine in a one‐pot method, which generates the desired products. This protocol demonstrates wide substrate tolerance, including hitherto unused aromatic amines, to yield the corresponding pure aromatic β‐enaminones, which are subsequently converted into the 3‐acylindole derivatives under mild conditions.

Magnetic Co/Al2O3 catalyst derived from hydrotalcite for hydrogenation of levulinic acid to γ-valerolactone

The efficient hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) over a hydrotalcite-derived non-precious metal Co/Al2O3 catalyst was achieved. Its core-shell structure and a strong interaction between Co and Al species stabilized the Co particles against leaching and sintering. This magnetic non-precious metal catalyst showed a comparable catalytic performance to a commercial Ru/C for the liquid hydrogenation of LA. It was easily separated from the reaction medium with an external magnet. The catalyst exhibited excellent recyclability, complete LA conversion and >99% GVL selectivity, and would be useful in a large scale biorefinery.

Palladium-catalyzed synthesis of indole-3-alkynones via direct carbonylation of indoles

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 °C). 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.

Carbonylative diversification of unactivated heteroaromatic compounds

The past decades have witnessed tremendous development in the field of carbonylative functionalization of aromatic compounds. In this context, various heterocycles could be directly utilized as simple starting materials to generate carbonyl group containing target molecules. This methodology has practical values, as the corresponding products could be used as useful building blocks in the synthesis of biologically active compounds. In this short review, we summarize the very recent development of this type of carbonylation reaction.