Palladium-Catalyzed Three-Component Dearomatization/Sulfonylation Cascade

Palladium-Catalyzed Domino Heck/Decarboxylative Cyanomethylation of Indoles and Alkenes with Cyanoacetate Salts

A palladium-catalyzed reaction of indoles with cyanoacetate salts enables the synthesis of 2,6-disubstituted indolines via tandem dearomatization/decarboxylative cyanomethylation. Remarkably, this is the first example of indole difunctionalization at the C2 and C6 positions. Moreover, this methodology extends to the palladium-catalyzed cyclization/decarboxylative cyanomethylation of aryl halide-tethered alkenes.

A Cascade C(sp3)-H Annulation Involving C(alkyl),C(alkyl)-Palladacycle Intermediates

C-H bond functionalization involving C,C-palladacycle intermediates provides a unique platform for developing novel reactions. However, the vast majority of studies have been limited to the transformations of C(aryl),C-palladacycles. In sharp contrast, catalytic reactions involving C(alkyl),C(alkyl)-palladacycles have rarely been reported. Herein, we disclose an unprecedented cascade C(sp3)-H annulation involving C(alkyl),C(alkyl)-palladacycles. In this protocol, alkene-tethered cycloalkenyl bromides undergo intramolecular Heck/C(sp3)-H activation to generate C(alkyl),C(alkyl)-palladacycles, which can be captured by α-bromoacrylic acids to afford tricyclic fused pyridinediones. In addition, this strategy can also be applied to indole-tethered cycloalkenyl bromides to construct pentacyclic fused pyridinediones via suquential Heck dearomatization/C(sp3)-H activation/decarboxylative cyclization. Notably, the removal of α-bromoacrylic acids in the reaction of alkene-tethered cycloalkenyl bromides can build an interesting tricyclic skeleton containing a four-membered ring. Preliminary mechanistic experiments indicate that five-membered C(alkyl),C(alkyl)-palladacycles serve as the key intermediates. Meanwhile, density functional theory (DFT) calculations have provided insights into the reaction pathway.

Palladium-Catalyzed Dearomative Heck/C(sp2)-H Activation/Decarboxylative Cyclization of C2-Tethered Indoles

Until now, palladium-catalyzed dearomative Heck reactions of indoles were largely limited to β-H elimination and nucleophilic capture of the transient alkyl-Pd(II) species. Herein, we disclose a novel palladium-catalyzed dearomative Heck/C(sp2)-H activation/decarboxylative cyclization of C2-tethered indoles. In this protocol, the alkyl-Pd(II) species formed by dearomatization of C2-tethered indoles is not terminated by common β-H elimination or nucleophilic capture, but rather generates C,C-palladacycle via C-H activation. The latter is intercepted by α-bromoacrylic acids to produce pentacyclic and heptacyclic fused indolines.

Recent advances in palladium-catalyzed sulfonylation via SO2 insertion

The importance of sulfonyl-group-containing compounds, such as sulfonamides, sulfones, sulfinate esters, and sulfonyl fluorides, in pharmaceuticals, bioactive molecules, and natural products cannot be overstated. The new development of palladium-catalyzed sulfonylation via SO2 insertion represents a crucial advancement in organic synthesis, enabling the direct α,α-difunctionalization of SO2 and providing efficient access to an array of structure-diverse sulfonyl-containing compounds. Although there have been numerous reviews about SO2 insertion, many of them only cover specific aspects of palladium-catalyzed reactions, leading to an oversight of some important works. Besides, these reviews often lack detailed discussions and systematic conclusion on reaction mechanisms, and fail to comprehensively summarize the significant research achievements in palladium-catalyzed reactions over the past few years. Herein, we aim to systematically consolidate the recent advances in palladium-catalyzed sulfonylation via SO2 insertion, elucidate the underlying reaction mechanism, and highlight some unsolved challenges in this segment. This review seeks to serve as a valuable resource for researchers, assisting in the continued development of palladium-catalyzed sulfonylation methodologies.