Palladium-catalysed direct arylations of NH-free pyrrole and N-tosylpyrrole with aryl bromides

Design of a Mesoionic Janus-type Dicarbene

A versatile synthetic strategy for the preparation of homo- and heterobimetallic complexes bearing an unprecedented mesoionic Janus-type diNHC is presented. Moreover, its electronic property is evaluated, and a preliminary catalytic application in the direct diarylation of 1-methylpyrrole is demonstrated.

Palladium-Catalysed Intermolecular Direct C–H Bond Arylation of Heteroarenes with Reagents Alternative to Aryl Halides: Current State of the Art

Abstract:

Abstract: This unprecedented review with 322 references provides a critical up-to-date picture of the Pd-catalysed intermolecular direct C–H bond arylation of heteroarenes with arylating reagents alternative to aryl halides that include aryl sulfonates (aryl triflates, tosylates, mesylates, and imidazole-1-sulfonates), diaryliodonium salts, [(diacetoxy)iodo]arenes, arenediazonium salts, 1-aryltriazenes, arylhydrazines and N’-arylhydrazides, arenesulfonyl chlorides, sodium arenesulfinates, arenesulfinic acids, and arenesulfonohydrazides. Particular attention has been paid to summarise the preparation of the various arylating reagents and to highlight the practicality, versatility, and limitations of the various developed arylation protocols, also comparing their results with those achieved in analogous Pd-catalysed arylation reactions involving the use of aryl halides as electrophiles. Mechanistic proposals have also been briefly summarised and discussed. However, data concerning Pd-catalysed direct C–H bond arylations involving the C–H bonds of aryl substituents of the examined heteroarene derivatives have not been taken into account.

Recent Advances in Functionalization of Pyrroles and their Translational Potential

Among the known aromatic nitrogen heterocycles, pyrrole represents a privileged aromatic heterocycle ranging its occurrence in the key component of "pigments of life" to biologically active natural products to active pharmaceuticals. Pyrrole being an electron-rich heteroaromatic compound, its predominant functionalization is legendary to aromatic electrophilic substitution reactions. Although a few excellent reviews on the functionalization of pyrroles including the reports by Baltazzi in 1963, Casiraghi and Rassu in 1995, and Banwell in 2006 are available, they are fragmentary and over fifteen years old, and do not cover the modern aspects of catalysis. A review covering a comprehensive package of direct functionalization on pyrroles via catalytic and non-catalytic methods including their translational potential is described. Subsequent to statutory yet concise introduction, the classical functionalization on pyrroles using Lewis acids largely following an ionic mechanism is discussed. The subsequent discussion follows the various metal-catalyzed C-H functionalization on pyrroles, which are otherwise difficult to implement by Lewis acids. A major emphasize is given on the radical based pyrrole functionalization under metal-free oxidative conditions, which is otherwise poorly highlighted in the literature. Towards the end, the current development of pyrrole functionalization under photocatalyzed and electrochemical conditions is appended. Only a selected examples of substrates and important mechanisms are discussed for different methods highlighting their scopes and limitations. The aromatic nucleophillic substitution on pyrroles (being an electron-rich heterocycle) happened to be the subject of recent investigations, which has also been covered accentuating their underlying conceptual development. Despite great achievements over the past several years in these areas, many challenges and problems are yet to be solved, which are all discussed in summary and outlook.

Decarboxylative arylation of substituted pyrroles N-protected with 2-(trimethylsilyl)ethoxymethyl (SEM)

Palladium-catalyzed decarboxylative arylation is reported using pyrroles N-protected with the 2-(trimethylsilyl)ethoxymethyl (SEM) group and featuring 2-, 3-, and 4-substituents about the pyrrolic framework. In contrast to N-protected pyrroles previously used in decarboxylative arylation, the use of SEM allows deprotection under mild conditions.

Highly Efficient Preparation of Amides from Aminium Carboxylates Using N-(p-toluenesulfonyl) Imidazole

Treatment of aminium carboxylates with N-(p-toluenesulfonyl)imidazole in the presence of triethylamine in DMF at 100 °C afforded the corresponding amides in good to excellent yields. N-(p-Toluenesulfonyl)imidazole proved to be a highly efficient coupling reagent for the preparation of numerous structurally diverse primary, secondary and tertiary amides.

Regioselectivity in palladium-catalysed direct arylation of 5-membered ring heteroaromatics

In the past few years, several results using modified catalysts and new reaction conditions have been reported permitting better control of the regioselectivity of Pd-catalysed arylations.