Amidation of Enones via Beckmann Rearrangement.

The Beckmann reaction is one of the most atom-economical methods for the preparation of amides from ketones. Unlike ketones, the multiple competing reactivities of enones as well as the requirement of demanding reaction conditions for in situ generation of oximes have severely impacted the application of this reaction for the preparation of α,ß-unsaturated amides. Herein, we describe the first chemoselective method for the direct conversion of enones to the corresponding α,ß-unsaturated amides using N-Boc-O-tosylhydroxylamine.

Copper(II) nanodots stabilized on Cassia fistula galactomannan: preparation and catalytic application towards fast solvent-free Biginelli reactions.

New Cu(II) nanodots have been developed using biopolymeric polysaccharide galactomannan. The nanocatalyst Cu(II)NDs@CFG has been developed through a one-step clean and sustainable reaction of Cassia fistula galactomannan and CuSO4·5H2O in an aqueous medium. The catalyst Cu(II)NDs@CFG is well characterized by FT-IR, FE-SEM, EDS, ICP-MS, HR-TEM, XPS, XRD, TGA and BET analysis. This is the first example of preparing copper nanodots by using polysaccharide galactomannan as a supporting template to form copper nanodots in water. Moreover, the copper nanodots act as a potential nanocatalyst for multicomponent Biginelli reactions. A simple, one pot, efficient and environmentally benign synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones has been achieved with wide variety of aldehydes, ß-dicarbonyl compounds and urea or thiourea indicating the good tolerance of the catalyst towards various functionalities. The presented work has several merits in terms of economy which include easy operation, complete avoidance of toxic organic solvents and expensive catalysts, simple work-up, less reaction time, and excellent yields.

Organocatalytic access to 3-pyridylphosphonates from vinyl phosphonates and aldehydes.

The preparation of 3-phosphorylated pyridines has remained the most challenging compared to the corresponding 2- or 4-functionalized pyridines. Herein, an unprecedented amino-organocatalyzed direct synthesis of 3-pyridylphosphonates from vinylphosphonates and aldehydes has been achieved. This allows access to a wide range of multi-substituted phosphorylated pyridines in excellent yields under transition metal-free conditions.

Cassia fistula galactomannan stabilized copper nanocatalyst as an efficient, recyclable heterogeneous catalyst for the fast clickable [3+2] Huisgen cycloadditions in water.

In this study, we have first time investigated the synthesis of copper nanocatalyst by using biopolymer galactomannan, naturally extracted from Cassia fistula pods. The methodology involved for the preparation of copper nanocatalyst is economical, efficient, environment friendly, and did not involve further processing for stabilization or reduction of copper nanoparticles. The morphology and structural characterization of the nanocatalyst was performed by using different techniques such as FT-IR, 1H NMR, SEM, EDX, HR-TEM, XRD, XPS, ICP-MS, BET, and TGA analysis. The prepared copper nanocatalyst is applied for the click [3+2] Huisgen cycloadditions of various azides and alkynes, employing water as environmentally benign solvent. In comparison to earlier reported methods, our method requires lowest catalyst loading, less reaction time, excellent yields and have wide substrate scope. Additionally, the catalyst was easily recovered by simple filtration and recycled at least ten consecutive times without any appreciable loss of efficiency and selectivity. The effect of mannose and galactose (Man/Gal) ratio of Cassia fistula galactomannan on the catalytic activity were also investigated.

Iodobenzene-Catalyzed Synthesis of Fully Functionalized NH-Pyrazoles and Isoxazoles from α,ß-Unsaturated Hydrazones and Oximes via 1,2-Aryl Shift.

An iodine(III)-catalyzed general method for the synthesis of fully functionalized NH-pyrazoles and isoxazoles from α,ß-unsaturated hydrazones and oximes, respectively, via cyclization/1,2-aryl shift/aromatization/detosylation, has been developed. The reaction progresses through an anti-Baldwin 5-endo-trig cyclization. It gives direct access to an advanced intermediate for the preparation of valdecoxib and parecoxib, drugs used for COX-inhibition. In addition, a method for N-alkynylation of pyrazoles has also been developed in the presence of TIPS-EBX.

Construction of Highly Functionalized C4-Oxyacylated and Aminated Pyrazolines.

Pyrazolines and pyrazolones are prevalent cores in drugs and bioactive molecules. Functionalizing them with heteroatoms on the ring improves or expands their clinical efficacy. However, a general method to selectively heterofunctionalize them at C4 and C5 is still elusive. Herein, we have demonstrated an iodine(III)-mediated construction of C4-heterofunctionalized pyrazolines from α,ß-unsaturated hydrazones. The oxyacylated and aminated products, bearing a tertiary as well as a secondary stereocenter, were obtained via aza-Michael, followed by a C-O/C-N bond formation. A deprotection/oxidation sequence produced pyrazolones in a quantitative yield.

Novel Functionalized Spiro [Indoline-3,5'-pyrroline]-2,2'dione Derivatives: Synthesis, Characterization, Drug-Likeness, ADME, and Anticancer Potential.

A highly stereo-selective, one-pot, multicomponent method was chosen to synthesize the novel functionalized 1, 3-cycloaddition spirooxindoles (SOXs) (4a-4h). Synthesized SOXs were analyzed for their drug-likeness and ADME parameters and screened for their anticancer activity. Our molecular docking analysis revealed that among all derivatives of SOXs (4a-4h), 4a has a substantial binding affinity (∆G) -6.65, -6.55, -8.73, and -7.27 Kcal/mol with CD-44, EGFR, AKR1D1, and HER-2, respectively. A functional study demonstrated that SOX 4a has a substantial impact on human cancer cell phenotypes exhibiting abnormality in cytoplasmic and nuclear architecture as well as granule formation leading to cell death. SOX 4a treatment robustly induced reactive oxygen species (ROS) generation in cancer cells as observed by enhanced DCFH-DA signals. Overall, our results suggest that SOX (4a) targets CD-44, EGFR, AKR1D1, and HER-2 and induces ROS generation in cancer cells. We conclude that SOX (4a) could be explored as a potential chemotherapeutic molecule against various cancers in appropriate pre-clinical in vitro and in vivo model systems.

N-Heterocyclic Carbene-Catalyzed Enantioselective [3 + 2] Annulation of Enals with Vinyl Ketones.

An unprecedented N-heterocyclic carbene (NHC)-catalyzed enantioselective [3 + 2] annulation of enals with vinyl ketones has been achieved. Unlike chalcones, the ß-unsubstituted enones, namely, vinyl ketones, have remained challenging in terms of reactivity, especially enantioselectivity. The disubstituted cyclopentenes were obtained in good yields and excellent stereoselectivities in the presence of Ti(OiPr)4.

Reductive Alkenylation of Ketimines via Hydride Transfer from Aldehydes.

The first direct N-heterocyclic carbene (NHC)-catalyzed preparation of allylic amines bearing a quaternary center (α-tertiary amine) from isatin-derived ketimines in the presence of vinyl selenones and aldehydes is reported. This multicomponent reaction is expected to proceed via unprecedented in situ reduction of imines through a hydride transfer from the aldehydes.

Direct N-Me Aziridination of Enones.

The first direct general method for N-Me aziridination of electron-deficient olefins, enones, is described using N-methyl-O-tosylhydroxylamine as the aminating agent in the presence of a Cu(OTf)2 catalyst. The aziridination of vinyl ketones, hitherto unknown for N-Me as well as N-H, has been achieved efficiently. The open-flask reaction is stereospecific, operationally simple, and additive-free. It also efficiently affords N-H aziridinated products under a similar reaction condition.

A General Method for α-Oxyacylation of Vinyl Ketones Using Koser's Reagent.

A direct general method for the preparation of α-oxyacylated vinyl ketones using Koser's hypervalent iodine reagent is reported. A variety of acyloxy groups from long-chain aliphatic, aromatic, α,ß-unsaturated carboxylic acids have been installed efficiently for the first time. The oxyacylated adducts were used for the preparation of densely functionalized chiral δ-lactones and cyclopentenes using carbene organocatalysis.

Stitching Triazoles to Arenes via a Transition Metal-Free Aryne Diels-Alder/1,3-Prototropic Shift/Dehydrobromination Cascade.

The 1,2,3-triazole-fused polyaromatic frameworks are traditionally obtained through transition metal-catalyzed C-H/C-X arylation of the preinstalled triazoles at a very high temperature. Herein, a transition metal-free direct synthesis via an aryne Diels-Alder/1,3-prototropic shift/dehydrobromination cascade is reported. This method gives access to triazole-fused aromatics as well as the corresponding dihydrocarbocycles under mild reaction conditions.

Stereoselective Oxidative Rearrangement of Disubstituted Unactivated Alkenes Using Hypervalent Iodine(III) Reagent.

The stereoselective oxidative rearrangement of disubstituted unactivated olefins has been achieved using a hypervalent iodine(III) reagent. The aryl group undergoes 1,2-migration to give tert-α-arylated aldehydes (as acetals). The preparation of these aldehydes/acetals, especially containing a tert-benzylic stereocenter, has remained challenging. This migration-based method provides a complementary approach over the known α-substitution-based methods for accessing this class of molecules.

Global Access to 3/4-Phosphorylated Heterocycles via a Carbene-Catalyzed Stetter Reaction of Vinylphosphonates and Aldehydes.

The first global method for the preparation of 3-phosphorylated-pyrroles, -furans, -thiophenes, and 4-phosphorylated 2,5-dihydropyridazines is reported. To achieve this, the first protocol for the direct synthesis of α-phosphorylated 1,4-diketones has been developed through a carbene-catalyzed Stetter reaction of vinylphosphonates and aldehydes. This is the first synthetic method for accessing 4-phosphorylated 2,5-dihydropyridazines. This process is metal-free and produces multifunctionalized heterocycles.

Access to enantioenriched 4-phosphorylated δ-lactones from ß-phosphorylenones and enals via carbene organocatalysis.

N-heterocyclic carbene (NHC) catalyzed direct access to enantioenriched 4-phosphorylated δ-lactones from ß-phosphorylenones and enals has been achieved. The sterically demanding ß-phosphonate-substituted enones, having competing regiomeric reaction centres, have remained elusive so far in intermolecular cycloaddition reactions under NHC catalysis. All the products were obtained in excellent yield and enantioselectivity. These phosphorylated δ-lactones could be transformed into challenging multi-functionalized chiral esters and amides loaded with a ß-ketophosphonate functionality.

Carbene/Base-Mediated Redox Alkenylation of Isatins using ß-Substituted Organoselenones and Aldehydes.

Achieving several desired transformations in a single operation remains one of the obvious goals in the synthetic organic chemistry. Herein we developed a multicomponent reaction for the preparation of alkenylated oxyindoles, bearing a quaternary alcohol-derived ester, via an NHC-catalyzed redox reaction in the presence of ß-substituted vinyl selenones and aldehydes.

Construction of Phenanthrenes and Chrysenes from ß-Bromovinylarenes via Aryne Diels-Alder Reaction/Aromatization.

A highly efficient transition-metal-free general method for the synthesis of polycyclic aromatic hydrocarbons like phenanthrenes and chrysenes (and tetraphene) from ß-bromovinylarenes and arynes has been developed. The reactions proceed via an aryne Diels-Alder (ADA) reaction, followed by a facile aromatization. This is the first report on direct construction of chrysenes (and tetraphene) using the ADA approach. Unlike the literature method which is limited to only 9/10-substituted derivatives, this method gives access to a wide variety of functionalized phenanthrenes.

Direct N-H/ N-Me Aziridination of Unactivated Olefins Using O-(Sulfonyl)hydroxylamines as Aminating Agents.

Unactivated aziridines are the core substructures in a plethora of bioactive natural products and serve as building blocks in organic synthesis. Despite this, very limited methods are available to access them directly from olefins, as most of the known methods are devoted to their activated counterparts. Herein, we have developed a highly efficient Rh(II)-catalyzed method for the direct preparation of unactivated aziridines from olefins using O-(sulfonyl)hydroxylamines as the aminating agent. The reactions proceed with a high stereospecificity.

Carbene-Catalyzed Tandem [1,2]-Phospha-Brook/[1,4]-Phosphate Rearrangement: Access to α-Ketophosphates via Controlled Cross-Acyloin Condensation.

The first N-heterocyclic carbene (NHC)-organocatalytic tandem [1,2]-phospha-Brook/[1,4]-phosphate rearrangement is reported. Acyl phosphonates, unlike acyl silanes that are well-exploited, make entry as the acyl anion precursors under NHC catalysis. The reactions proceed with absolute chemoselectivity via cross-acyloin condensation between acyl phosphonates and aldehydes giving the products α-ketophosphates in good to excellent yields. The challenging (enolizable) aliphatic-aliphatic substrates coupling also furnished the desired product in a good yield.

Direct Construction of 2,3-Dihydroxy-2,3-diaryltetrahydrofurans via N-Heterocyclic Carbene/Base-Mediated Domino Reactions of Aromatic Aldehydes and Vinyl Selenone.

A one-pot, stereoselective construction of 2,3-dihydroxy-2,3-diaryltetrahydrofurans has been achieved via N-heterocyclic carbene (NHC)/base-mediated domino reactions of aldehydes and vinyl selenone. The products containing two contiguous quaternary hydroxyl functionalities among the three stereocenters are obtained advantageously as either acetals or ketals through the formation of five new chemical bonds in a single operation. This report constitutes an altogether different reactivity of vinyl selenone in comparison with the corresponding sulfones and phosphonates under NHC/base-mediated reactions.