Configurationally labile α-bromoacid derivatives for asymmetric preparation of heterocycles

α-Bromoacid derivatives are configurationally labile under various conditions, and the dynamic resolution of them has been recognized as an effective strategy in asymmetric synthesis. This article is a concise review of our efforts on the heteroannulation of α-bromoacid derivatives through nucleophilic substitution and subsequent ring formation with diverse carbon, nitrogen, oxygen, and sulfur nucleophiles. Chiral auxiliary (Xc)-bound α-bromoacid derivatives serve as versatile chiral building blocks for the direct incorporation of a two-carbon unit in cyclization reactions. Eight readily available chiral auxiliaries are investigated and identified to be suitable for the dynamic resolution of α-bromoacid derivatives. We have presented selected results about three distinct dynamic resolutions such as dynamic kinetic resolution (DKR), dynamic thermodynamic resolution (DTR) and crystallization induced dynamic resolution (CIDR) that have been successfully employed in the asymmetric synthesis of fourteen different scaffolds of six- or five-membered heterocycles.

Skeletal and Mechanistic Diversity in Ir-Catalyzed Cycloisomerizations of Allene-Tethered Pyrroles and Indoles

Pyrroles and indoles bearing N-allenyl tethers participate in a variety of iridium-catalyzed cycloisomerization processes initiated by a C-H activation step, to deliver a diversity of synthetically relevant azaheterocyclic products. By appropriate selection of the ancillary ligand and the substitution pattern of the allene, the reactions can diverge from simple intramolecular hydrocarbonations to tandem processes involving intriguing mechanistic issues. Accordingly, a wide range of heterocyclic structures ranging from dihydro-indolizines and pyridoindoles to tetrahydroindolizines, as well as cyclopropane-fused tetrahydroindolizines can be obtained. Moreover, by using chiral ligands, these cascade processes can be carried out in an enantioselective manner. DFT studies provide insights into the underlying mechanisms and justify the observed chemo- regio- and stereoselectivities.

Development of novel transition metal-catalyzed synthetic approaches for the synthesis of a dihydrobenzofuran nucleus: a review

The synthesis of dihydrobenzofuran scaffolds bears pivotal significance in the field of medicinal chemistry and organic synthesis. These heterocyclic scaffolds hold immense prospects owing to their significant pharmaceutical applications as they are extensively employed as essential precursors for constructing complex organic frameworks. Their versatility and importance make them an interesting subject of study for researchers in the scientific community. While exploring their synthesis, researchers have unveiled various novel and efficient pathways for assembling the dihydrobenzofuran core. In the wake of extensive data being continuously reported each year, we have outlined the recent updates (post 2020) on novel methodological accomplishments employing the efficient catalytic role of several transition metals to forge dihydrobenzofuran functionalities.

Transition-metal-catalyzed C-H bond alkylation using olefins: recent advances and mechanistic aspects

Transition metal catalysis has contributed immensely to C-C bond formation reactions over the last few decades, and alkylation is no exception. The superiority of such methodologies over traditional alkylation is evident from minimal reaction steps, shorter reaction times, and atom economy while also allowing control over regio- and stereo-selectivity. In particular, hydrocarbonation of alkenes has grabbed increased attention due its fundamental ability to effectively and selectively synthesise a wide range of industrially and pharmaceutically relevant moieties. This review attempts to provide a scientific viewpoint and a systematic analysis of the recent developments in transition-metal-catalyzed alkylation of various C-H bonds using simple and activated olefins. The key features and mechanistic studies involved in these transformations are described briefly.

Palladium-Catalyzed Decarboxylative O-Allylation of Phenols with γ-Methylidene-δ-valerolactones

A novel Palladium-Catalyzed decarboxylative O-allylation of phenols was developed, in which a γ-methylidene-δ- valerolactone (GMDVs) was found to be an efficient and selective allylation reagent, affording the target allyl phenyl...

Iridium-catalyzed enantioselective intramolecular hydroarylation of allylic aryl ethers devoid of a directing group on the aryl group

Although intramolecular hydroarylation is an attractive transformation of allylic aryl ethers, it has suffered from narrow substrate scope. We herein describe Ir/(S)-DTBM-SEGPHOS-catalyzed intramolecular hydroarylation of allylic aryl ethers. The reaction eliminates the structural requirement from the aryl group, affording 2,3-dihydrobenzofurans bearing a stereogenic carbon center at the C3 position with up to 99% enantiomeric excess.

Iridium-Catalyzed Hydroarylation via C-H Bond Activation

Hydroarylation reactions via C-H activation, which compensate for shortcomings of classical methods based on the Friedel-Crafts reaction, is one of the most attractive methods to synthesize substituted arenes. This Personal Account reviews our recent studies on iridium-catalyzed intermolecular hydroarylation of vinyl ethers, alkynes, bicycloalkenes, and 1,3-dienes, and intramolecular hydroarylation of m-allyloxyphenyl ketones, where asymmetric addition reactions are included. A cationic iridium catalyst, which is generated from chloroiridium [IrCl] and NaBAr^F ₄ [Ar^F =3,5-(CF₃ )₂ C₆ H₃ ], or a hydroxoiridium [Ir(OH)] complex is effective in catalyzing the hydroarylation depending on the substrates. 1,5-Cyclooctadiene (cod), chiral dienes, and conventional bisphosphines function as ligands controlling the high reactivity and selectivity of the catalysts in the hydroarylation. H/D exchange reaction of alkenes by use of a key intermediate of the hydroarylation reaction is also described.

Enantioselective Intermolecular Murai-Type Alkene Hydroarylation Reactions

Strategies that enable the efficient assembly of complex building blocks from feedstock chemicals are of paramount importance to synthetic chemistry. Building upon the pioneering work of Murai and co-workers in 1993, C–H-activation-based enantioselective hydroarylations of alkenes offer a particularly promising framework for the step- and atom-economical installation of benzylic stereocenters. This short review presents recent intermolecular enantioselective Murai-type alkene hydroarylation methodologies and the mechanisms by which they proceed.

1 Introduction

2 Enantioselective Hydroarylation Reactions of Strained Bicyclic Alkenes

3 Enantioselective Hydroarylation Reactions of Electron-Rich Acyclic Alkenes

4 Enantioselective Hydroarylation Reactions of Electron-Poor Acyclic Alkenes

5 Enantioselective Hydroarylation Reactions of Minimally Polarized Acyclic Alkenes

6 Conclusion and Outlook