Carbonylative synthesis and functionalization of indoles

Carbonylation processes have become widely recognized as a versatile, convenient, and low-cost method for the synthesis of high-value compounds. Given the great importance of heterocyclic compounds, the carbonylative approach has become increasingly important for their synthesis. In this mini-review, as a class of benzo-fused nitrogen-containing heterocyclic compounds, we summarized and discussed the recent achievements on the synthesis and functionalization of indole derivatives via carbonylative approaches.

Palladium-catalyzed intramolecular aza-Wacker-type cyclization of vinyl cyclopropanecarboxamides to access conformationally restricted aza[3.1.0]bicycles

A palladium(ii)-catalyzed intramolecular oxidative aza-Wacker-type reaction of vinyl cyclopropanecarboxamides to access a series of conformationally restricted highly substituted aza[3.1.0]bicycles is reported. The transformation proceeded through a typical aza-Wacker reaction mechanism to forge a new C-N bond with oxygen as the terminal oxidant. The desired fused heterocycles were obtained in moderate yields. The process is tolerant of a range of functional aryl groups under mild conditions.

Recent advances in the synthesis of pyrrolo[1,2-a]indoles and their derivatives

The pyrrolo[1,2-a]indole unit is a privileged heterocycle found in numerous natural products and has been shown to exhibit diverse pharmacological properties. Thus, recent years have witnessed immense interest from the synthesis community on the synthesis of this scaffold. In light of the ever-increasing demand for pyrrolo[1,2-a]indoles in drug discovery, this review provides an overview of recent synthesis methods for the preparation of pyrrolo[1,2-a]indoles and their derivatives. The mechanistic pathway and stereo-electronic factors affecting the yield and selectivity of the product are briefly explained. Furthermore, we have attempted to demonstrate the utility of the developed methods in the synthesis of bioactive molecules and natural products, wherever offered.

Isoindolinone Synthesis via One-Pot Type Transition Metal Catalyzed C-C Bond Forming Reactions

Isoindolinone structure is an important privileged scaffold found in a large variety of naturally occurring as well as synthetic, biologically and pharmaceutically active compounds. Owing to its crucial role in a number of applications, the synthetic methodologies for accessing this heterocyclic skeleton have received significant attention during the past decade. In general, the synthetic strategies can be divided into two categories: First, direct utilization of phthalimides or phthalimidines as starting materials for the synthesis of isoindolinones; and second, construction of the lactam and/or aromatic rings by different catalytic methods, including C-H activation, cross-coupling, carbonylation, condensation, addition and formal cycloaddition reactions. Especially in the last mentioned, utilization of transition metal catalysts provides access to a broad range of substituted isoindolinones. Herein, the recent advances (2010-2020) in transition metal catalyzed synthetic methodologies via formation of new C-C bonds for isoindolinones are reviewed.

One-Step Synthesis of Isoindolo[2,1-a]indol-6-ones via Tandem Pd-Catalyzed Aminocarbonylation and C-H Activation

A unified catalytic system for tandem Pd-catalyzed carbonylation and C-C cross-coupling via C-H activation was designed. The proposed cascade reaction allows a facile one-step construction of a tetracyclic isoindoloindole skeleton, in which three new C-C/C-N bonds are simultaneously formed. In detail, the carbonylation of aryl dibromides with indoles and C-H activation of in situ formed N-(2'-bromoaroyl)-indole provide biologically relevant 6H-isoindolo[2,1-a]indol-6-ones from commercially available substrates. The aminocarbonylation step in the proposed tandem reaction utilizes glyoxylic acid monohydrate as an environmentally friendly CO surrogate.

A Pd-catalyzed domino Larock annulation/dearomative Heck reaction

A highly efficient synthesis of indolines from N-bromobenzoyl o-iodoanilines and alkynes is developed via a domino Larock annulation/dearomative Heck reaction.

One-Pot Synthesis of Indole-3-acetic Acid Derivatives through the Cascade Tsuji-Trost Reaction and Heck Coupling

A practical palladium-mediated cascade Tsuji-Trost reaction/Heck coupling of N-Ts o-bromoanilines with 4-acetoxy-2-butenonic acid derivatives using a Pd(OAc)₂/P( o-tol)₃/DIPEA system is described for a straightforward synthesis of indole-3-acetic acid derivatives. This methodology was successfully applied to synthesize various substituted indole/azaindole-3-acetic acid derivatives and Almotriptan, which is a drug for the acute treatment of migraines. Moreover, a plausible cyclization mechanism has been proposed.

Reactivity of alkynylindole-2-carboxamides in [Pd]-catalysed C–H activation and phase transfer catalysis: formation of pyrrolo-diindolones vs. β-carbolinones

[Pd]-Catalysed reaction of 3-alkynylindole-2-carboxamidesviaC–H activation leads to pyrrolodiindolones; in contrast, under phase-transfer catalysis, the same precursors afford β-carbolinones.