Transition-Metal-Catalyzed Directed C-H Functionalization in/on Water.

Directing group assisted C-H bond functionalization using transition-metal-catalysis has emerged as a reliable synthetic tool for the construction of regioselective carbon-carbon/heteroatom bonds. Off late, "in/on water directed transition-metal-catalysis", though still underdeveloped, has appeared as one of the prominent themes in sustainable organic chemistry. This article covers the advancements, mechanistic insights and application of the sustainable directed C-H bond functionalization of (hetero)arenes in/on water in the presence of transition-metal-catalysis.

Palladium-Catalyzed Annulative Coupling of Spirovinylcyclopropyl Oxindoles with p-Quinone Methides.

Pd-catalyzed annulative coupling of spirovinylcyclopropyl oxindoles with p-quinone methides has been accomplished via cascade carbon-carbon bond formation to afford bis-spirooxindole scaffolds. The mild reaction conditions, diastereoselectivity, functional group diversity, post-synthetic transformations, and mechanistic studies using DFT calculations are the important practical features.

Cobalt-Catalyzed Stereospecific C-N/C-O Bond Formation of Oxiranes with Diaziridines.

Co-catalyzed stereospecific C-N and C-O bond formation of oxiranes with diaziridines has been accomplished to furnish tetrahydro-[1,3,4]-oxadiazines at room temperature. Optically active oxiranes can be coupled with high optical purities (>96% ee). Stereoselectivity, functional group tolerance, mechanistic studies using DFT, and natural product modification are the important practical features.

Bi-Catalyzed 1,2-Reactivity of Spirocyclopropyl Oxindoles with Dithianediol: Access to Spiroheterocycles.

The efficient Bi-catalyzed 1,2-reactivity of spirocyclopropyl oxindoles has been disclosed with dithianediols as the sulfur surrogate to furnish spiroheterocycles at moderate temperature. The procedure provides a potential approach for the construction of spirotetrahydrothiophene scaffolds with functional group diversity. The catalytic 1,2-reactivity of cyclopropanes, mechanistic studies using density functional theory studies, diastereoselectivity, and additive-free mild conditions are the important practical features.

Expedient Ni-catalyzed C-H/C-H cross-dehydrogenative coupling of aryl amides with azoles.

A nickel-catalyzed C-H heteroarylation of arenes has been described using a removable oxazoline-aniline derived directing group. Utilization of an inexpensive nickel(II)-catalyst, substrate scope, functional group diversity and late-stage functionalization of xanthine-derived commercial drugs are the important practical features.

Pd-catalyzed bidentate auxiliary assisted remote C(sp3)-H functionalization.

Pd-catalyzed C-H functionalisation affords effective synthetic tools to construct C-C and C-X bonds. Despite the challenges, the distal functionalization of C(sp3)-H bonds has witnessed significant developments and the use of bidentate auxiliaries has garnished this area by providing an opportunity to control reactivity as well as selectivity beyond proximal sites. This article covers the recent developments on the Pd-catalyzed bidentate auxiliary-assisted distal C(sp3)-H functionalization and is categorized based on the nature of functionalizations.

Transition-Metal-Catalyzed Directing Group Assisted (Hetero)aryl C-H Functionalization: Construction of C-C/C-Heteroatom Bonds.

Transition-metal-catalyzed C-H functionalization is one of the fascinating scientific fronts in organic synthesis for the formation of conjugated arenes and has emerged as a benchmark to revolutionize the synthetic enterprise since past decades. In this realm, chelation-guided functionalization of C-H bonds using an exogenous directing group has received considerable attention recently for the expedient regioselective construction of C-C and C-heteroatom bonds as an efficient and sustainable alternative. This article outlines our contribution towards a wide variety of transformations that have been achieved by the directed C-H functionalization through the fine tuning of catalytic systems.

The transition-metal-catalyzed stereoselective ring-expansion of vinylaziridines and vinyloxiranes.

The transition-metal-aided stereoselective construction of sp3-carbon-rich heterocyclic scaffolds using strained-ring systems has received considerable attention in recent years due to the prominent presence of these scaffolds in myriad natural products, bioactive molecules, and pharmaceutical components. In this area, the catalytic ring-enlargement of vinylaziridines and vinyloxiranes plays a predominant role when synthesizing high sp3-content biorelevant heterocyclic compounds. This article aims to portray recent advancements in the ring-expansion of vinylaziridines and vinyloxiranes for accessing densely functionalized stereoselective heterocycles that have been developed over the past five years, with an emphasis on the substrate scopes and mechanistic insights into the key methodologies, and it is arranged based on the transition metals used and the ring sizes of the heterocyclic scaffolds.

Pd-Catalyzed sp3 C-H alkoxycarbonylation of 8-methylquinolines using Mo(CO)6 as a CO surrogate.

A Pd(ii)-catalyzed three-component sp3 C-H alkoxycarbonylation of 8-methylquinonlines (8-MQs) with alcohols is accomplished using the colorless crystalline Mo(CO)6 as a CO source. The protocol is compatible with a wide range of 8-MQs and alcohols, furnishing the carbonylated adducts in moderate to good yields. The substrate scope, functional group tolerance and natural product mutation are the important practical features.

Recent Advances in Stereoselective Ring Expansion of Spirocyclopropanes: Access to the Spirocyclic Compounds.

Spirocyclopropane represents a privileged structural scaffold for accessing synthetic libraries of densely functionalized spirocarbo- and heterocyclic compounds. Due to the ubiquity of spirocyclic motifs as a potent pharmacophore in natural products and pharmaceuticals, recent years have witnessed significant advances in developing synthetic strategies that exploits carbon-carbon bond scission in spirocyclopropanes. This paper summarizes the recent developments in stereoselective ring expansion of spirocyclopropanes in diversity-oriented synthesis and highlights the synthetic as well as mechanistic rationale of those methodologies. This review also encompasses the applicability of the protocols in bioactive natural product syntheses.

Transition-Metal-Free Stereospecific Oxidative Annulative Coupling of Indolines with Aziridines.

Tandem C-N bond formation for the oxidative annulation of indolines with aziridines is accomplished employing the combination of DDQ and NaOCl at ambient conditions. Optically active aziridine can be coupled with high enantiomeric purity (>99% ee). The substrate scope, stereocontrol with the enantioenriched substrate, and scale-up are the important practical advantages.

Expedient iron-catalyzed stereospecific synthesis of triazines via cycloaddition of aziridines with diaziridines.

Iron-catalyzed stereospecific [3+3]-annulation of aziridines with diaziridines is described to furnish [1,2,4]-triazines in high yield at room temperature. The use of an inexpensive iron salt catalyst, substrate scope and enantiomeric purity are the important practical features.

Ruthenium(II)-Catalyzed Positional Selective C-H Oxygenation of N-Aryl-2-pyrimidines.

Efficient Ru-catalyzed regioselective C-H oxygenation of N-aryl-2-pyrimidines is described with aryl carboxylic acids in the presence of AgSbF6 as an additive and Ag2CO3 as an oxidant. The reaction can be extended to alkyl, heteroaryl, and α,ß-unsaturated carboxylic acids. The regioselectivity, broad substrate scope, and functional group tolerance are the significant practical advantages.