Palladium-Catalyzed C-H Olefination of Imidazo[1,2a] pyridine Carboxamide in Aqueous Ethanol under Oxygen.

The advancement of sustainable chemistry and changes in the economy are strongly intertwined. Reaction time, cost savings, moderate temperatures, and generation of the fewest byproducts are frequently achieved by using catalytic processes. Herein, we report the C-H olefination of imidazo[1,2a] pyridine carboxamides with various acrylates in the presence of Pd (OAc)2 with O2 as the oxidant in aqueous ethanol rather than using non-ecofriendly solvents. The C-H activation features most user-friendly reaction conditions, excellent yield as well as plenty substrate scope and applicable for C-H deuteriation of the corresponding heteroarenes with D2O. Experimental mechanistic studies indicate that C-H activation step succeeded after formation of tetra coordinated square planer Pd-substrate adduct.

Palladium-Catalyzed Regiodivergent C-H Olefination of Imidazo[1,2a]pyridine Carboxamide and Unactivated Alkenes.

Despite remarkable successes in linear and branched vinyl (hetero) arene synthesis, regiodivergent C-H olefination with a single catalytic system has remained underdeveloped. Overcoming this limitation, a Pd/MPAA-catalyzed regiodivergent C-H olefination of imidazo[1,2a] pyridine carboxamides with unactivated terminal alkenes to generate branched and linear olefinated products depending upon the electronic nature of alkenes is reported herein. Moreover, this protocol can be applied for C-H deuteriation of the corresponding heteroarenes with D2 O as deuterium source. Preliminary experimental studies combined with computational investigations (DFT studies) suggest that regiodivergent olefination can be controlled by olefin insertion and ß-hydride elimination steps.

O-Benzoylhydroxylamines: A Versatile Electrophilic Aminating Reagent for Transition Metal-Catalyzed C-N Bond-Forming Reactions.

Owing to the prevalence of nitrogen-containing compounds in natural products and important pharmaceutical agents, chemists, have actively searched for the development of efficient and selective methodologies allowing for the facile construction of carbon-nitrogen bonds. Over the last decade, transition metal-catalyzed C-N bond construction via electrophilic amination reaction has emerged as an attractive approach for the synthesis of various organic molecules and pharmaceuticals. Particularly, O-benzoylhydroxylamines as an electrophilic aminating agent have proven to be the best and most widely used in both academic and industrial research. In this review, we highlight the key contributions to the recent transition metal-catalyzed C-N bond formation reactions using O-benzoylhydroxylamines as an aminating agent and their relevant mechanistic insights.

Microwave-Assisted Green Synthesis of Carbon Quantum Dots Derived from Calotropis Gigantea as a Fluorescent Probe for Bioimaging.

An eco-friendly, cost-effective, and convenient approach for synthesizing biocompatible fluorescent carbon quantum dots (CQDs) from the leaf extract of the medicinal plant Calotropis gigantea, commonly known as crown flower, has been demonstrated in this work. Fluorescence quantum yields of up to 4.24 percent were observed in as-synthesized CQDs. The size distribution of the as-synthesized CQDs varied from 2.7 to 10.4 nm, with a significant proportion of sp2 and sp3 carbon groups verified by nuclear magnetic resonance analysis. The zeta potential of as-synthesized CQDs was measured to be -13.8 mV, indicating the existence of a negatively charged surface with incipient instability in aqueous suspension. Furthermore, as an alternative to organic or synthetic dyes, the development of simple, inexpensive, and non-destructive fluorescence-based staining agents are highly desired. In this regard, as-synthesized CQDs have shown remarkable fluorescent staining capabilities in this work and might be utilised as a suitable probe for optical and bio-imaging of bacteria, fungi, and plant cells.

Energy Transfer Photocatalytic Radical Rearrangement in N-Indolyl Carbonates.

A new type of sp3-like N-centered radical has been generated by selective energy transfer catalysis. Upon photoexcitation, homolytic N-O bond cleavage of N-indolyl carbonate in the presence of an Ir complex produced N- and O-centered radicals. The high spin density at the C3 position of indole led to radical recombination with the O-centered radical, affording valuable 3-oxyindole derivatives without decarboxylation. Transformations of the desired products into various molecules were also demonstrated.

Rhodium-Catalyzed meta-C-H Functionalization of Arenes.

Rhodium-catalyzed ortho-C-H functionalization is well known in the literature. Described herein is the Xphos-supported rhodium catalysis of meta-C-H olefination of benzylsulfonic acid and phenyl acetic acid frameworks with the assistance of a para-methoxy-substituted cyano phenol as the directing group. Complete mono-selectivity is observed for both scaffolds. A wide range of olefins and functional groups attached to arene are tolerated in this protocol.

Remote para-C-H Functionalization of Arenes by a D-Shaped Biphenyl Template-Based Assembly.

Site-selective C-H functionalization has emerged as an efficient tool in simplifying the synthesis of complex molecules. Most often, directing group (DG)-assisted metallacycle formation serves as an efficient strategy to ensure promising regioselectivity. A wide variety of ortho- and meta-C-H functionalizations stand as examples in this regard. Yet despite this significant progress, DG-assisted selective para-C-H functionalization in arenes has remained unexplored, mainly because it involves the formation of a geometrically constrained metallacyclic transition state. Here we report an easily recyclable, novel Si-containing biphenyl-based template that directs efficient functionalization of the distal p-C-H bond of toluene by forming a D-shaped assembly. This DG allows the required flexibility to support the formation of an oversized pre-transition state. By overcoming electronic and steric bias, para-olefination and acetoxylation were successfully performed while undermining o- and m-C-H activation. The applicability of this D-shaped biphenyl template-based strategy is demonstrated by synthesizing various complex molecules.

Palladium(II)-Catalyzed meta-C-H Olefination: Constructing Multisubstituted Arenes through Homo-Diolefination and Sequential Hetero-Diolefination.

Divinylbenzene derivatives represent an important class of molecular building blocks in organic chemistry and materials science. Reported herein is the palladium-catalyzed synthesis of divinylbenzenes by meta-C-H olefination of sulfone-based arenes. Successful sequential olefinations in a position-selective manner provided a novel route for the synthesis of hetero-dialkenylated products, which are difficult to access using conventional methods. Additionally, 1,3,5-trialkenylated compounds can be generated upon successful removal of the directing group.

Meta-selective arene C-H bond olefination of arylacetic acid using a nitrile-based directing group.

A nitrile-based template attached with a phenylacetic acid framework promoted meta-selective C-H bond olefination. This palladium-catalyzed protocol is applicable to a wide range of substituted phenylacetic acids and tolerates a variety of functional groups. The versatility of this operationally simple method has been demonstrated through drug diversification.

Ag(I)-catalyzed regioselective ring-opening of N-tosylaziridine and N-tosylazetidine with S-, O-, and N-nucleophiles and tethered dinucleophiles.

[Ag(COD)(2)]PF(6) catalyzes the ring-opening of N-tosylaziridines and -azetidines with alcohols, amines, thiols, and related tethered 1,2-ethane dinucleophiles. Initial rate studies and DFT-based evaluation of stepwise energetics suggest an inverse relationship between the nucleophilic reactivity of a heteroatom donor and its binding affinity to cationic Ag(I).

Silver(I)-diene complexes as versatile catalysts for the C-arylation of N-tosylaziridines: mechanistic insight from in situ diagnostics.

Silver(I) complex [Ag(diene)(2)](+)Y(-) (where diene = cyclooctadiene, norbornadiene, and 1,3-cyclohexadiene; Y(-) = PF(6)(-), BF(4)(-)) efficiently catalyzes the arylation of N-tosylaziridines with arenes and heteroarenes under ambient condition to provide the corresponding beta-aryl amine derivatives with excellent regioselectivity. To understand the nature of substrate activation, and initial bond breaking/making steps, the following studies were conducted with the help of in situ NMR ((1)H, (31)P, (109)Ag) and ESI-MS probe: (I) evaluation of Hammett reaction constant (rho); (II) correlation of initial rate (k) versus cone angle (theta) of ligand L for reactions mediated by [Ag(COD)(2)]PF(6)/L (where L is a phosphine or a phosphite ligand); (III) identification of silver-arene intermediates in solution; and (IV) correlation of initial rate (k) with Delta(HOMO-LUMO) of [Ag(diene)(2)]PF(6) obtained from preliminary DFT studies. Study I led to a rho-value of -0.586, indicating that the extent of electrophilic perturbation is considerably less than a typical Lewis acid catalyzed process. Study II indicated that initial rate (k) increases with concomitant increase in theta, as well with Delta(31)P((complex-ligand)), which corroborates to a mechanism involving prior ligand dissociation. Study III showed the plausible formation of [Ag(diene)(arene)](+) and [Ag(arene)(2)](+) as reactive species in solution. Study IV showed that the dependence of initial rate (k) with diene ligand is in the order COD > NBD > CHD; which corresponds well with the order of hardness of the respective Ag(I) complexes.

Silver(I)-catalyzed dual activation of propargylic alcohol and aziridine/azetidine: triggering ring-opening and endo-selective ring-closing in a cascade.

[Ag(COD)(2)]PF(6) catalyzes the reaction between propargyl alcohols and N-tosylaziridines/azetidines leading to a diverse range of N,O-heterocycles, namely, oxazines, oxazepines, and oxazocines via ring-opening and ring-closing in a cascade.