Base-promoted multicomponent synthesis of 1,2,4-triazole-based hybrids from 1,3-diones, β-nitrostyrenes, and hydrazones.

Herein, we report a metal-free, base-promoted route for the synthesis of hybrid molecular scaffolds in which various 1,3-diones and 1,2,4-triazoles are linked by a benzyl bridge. This three-component, one-pot reaction was accomplished by first treating 4-hydroxycoumarin, -β-nitrostyrene, and aldehyde hydrazone in the presence of sodium carbonate. Further, this protocol was successfully expanded to other 1,3-diones, such as dimedone and 4-hydroxy-2-quinolone.

Copper-catalyzed aerobic annulation of hydrazones with dienones: an efficient route to pyrazole-linked hybrid molecules.

A copper-catalyzed aerobic [3 + 2] annulation reaction to access various pyrazole-bound chalcones starting from readily available and cost-effective hydrazones and dienones is reported. These pyrazole-bound chalcones were further utilized effectively to prepare a series of pyrazole-linked hybrid molecules, such as pyrazole-pyrazoline, pyrazole-aziridine, and pyrazole-pyridine hybrids by efficient simple transformations. Synthetically challenging hybrid molecules were obtained in a simple, two-step process with high atom economy under aerobic copper catalysis.

Metal-Free Bisamidation of -Tosylhydrazones with Carboxylic Acids Promoted by Tetrabutylammonium Iodide and -Butyl Hydroperoxide.

A versatile reaction between -tosylhydrazones and carboxylic acids to access bisamides is reported. This metal-free, room-temperature reaction was catalyzed by TBAI, while TBHP served as the oxidant. Broad substrate scope and good functional group tolerance are the key features of the strategy.

Progress in copper-catalysed/mediated intramolecular dehydrogenative coupling.

Transition metal-catalysed C-H functionalization reactions are one of the most efficient synthetic methodologies to construct carbon-carbon and carbon-heteroatom bonds. The initial developments in the field were largely dominated by expensive transition metal catalysts. However, in the past decade, the focus of the catalyst shifted to first-row transition metals and copper catalysis contributed significantly.

Synthesis of functionalized benzo[1,3]dioxin-4-ones from salicylic acid and acetylenic esters and their direct amidation.

Direct synthesis of 4-benzo[][1,3]dioxin-4-one derivatives from salicylic acids and acetylenic esters (both mono- and disubstituted) has been described. The reaction is mediated by CuI and NaHCO in acetonitrile. Room temperature amidation of the synthesized 1,3-benzodioxinones with primary amines readily afforded the corresponding salicylamides in moderate to good yields.

Aerobic oxidative coupling of arenes and olefins through a biomimetic approach.

Arenes and electron-deficient olefins can be oxidatively coupled through a biomimetic Pd(OAc)2-catalyzed transformation. C-H activation of the arene partner is effected under reaction conditions of low catalyst loading, normal oxygen pressure, and using p-benzoquinone and iron phthalocyanine as electron-transfer mediators (ETMs). By controlling catalyst loading, the reaction can be made selective for either mono- or diarylation.

Biomimetic aerobic oxidation of amino alcohols to lactams.

The right path: N-protected amino alcohols undergo aerobic and biomimetic oxidation to the corresponding lactams in the presence of a ruthenium catalyst and a combination of electron-transfer mediators under air (see scheme). The reaction was used for the synthesis of five-, six-, and seven-, membered lactams and showed good tolerance to a number of N-protecting groups.

NHC-catalysed annulation of enals to tethered dienones: efficient synthesis of bicyclic dienes.

Homoenolates generated from α,β-unsaturated aldehydes using NHC catalysis underwent facile addition to dibenzylidene cyclohexanone to afford bicyclic cyclopentenes as single diastereomers.

A novel pseudo four component reaction involving homoenolate for the synthesis of gamma-aminobutyric acid (GABA) derivatives.

Homoenolate generated from alpha,beta-unsaturated aldehydes by NHC catalysis underwent facile addition to conjugated sulfonimines, generated in situ, and subsequent methanolysis to afford protected GABA derivatives stereoselectively and in high yields, thus constituting a novel pseudo four component reaction.

Novel nucleophilic heterocyclic carbene mediated stereoselective conjugate addition of enals to nitrostyrenes via homoenolate.

A stereoselective Michael addition of homoenolate, generated from enals by nucleophilic heterocyclic carbene (NHC) catalysis, to beta-nitrostyrenes is reported for the first time. The products of this reaction obtained in good yields are of potential value in the synthesis of a variety of acyclic and heterocyclic compounds.

Nucleophilic heterocyclic carbene catalyzed annulation of enals to chalcones in methanol: a stereoselective synthesis of highly functionalized cyclopentanes.

Homoenolates generated from enals by nucleophilic heterocyclic carbene (NHC) catalysis undergo annulation with chalcones in methanol to afford methyl beta-hydroxycyclopentanecarboxylates, stereoselectively. Construction of four contiguous stereocenters in a stereoselective manner is noteworthy.

Recent advances in carbon-carbon bond-forming reactions involving homoenolates generated by NHC catalysis.

Homoenolate, a species containing anionic carbon beta to a carbonyl group or a moiety that can be transformed into a carbonyl group, is a potential three carbon synthon. Recent introduction of a protocol for the generation of homoenolate directly from enals by NHC (nucleophilic heterocyclic carbene) catalysis has made it possible to explore the synthetic utility of this unique reactive intermediate. The versatility of NHC-bound homoenolate is illustrated by its annulation with various carbonyl compounds leading to gamma-butyrolactones, spiro-gamma-butyrolactones, and delta-lactones.

Stereoselective synthesis of spirocyclopentanones via N-heterocyclic carbene-catalyzed reactions of enals and dienones.

Homoenolates generated from enals by nucleophilic heterocyclic carbene (NHC) catalysis undergo a conjugate addition/cyclization sequence with cyclic dienones, culminating in the efficient synthesis of spirocyclopentanones.

Carbon-nitrogen bond-forming reactions of dialkyl azodicarboxylate: a promising synthetic strategy.

Azodicarboxylates have found applications in electrophilic amination reactions and in pericyclic reactions. The nucleophilic trigger in Mitsunobu reactions, that is, the zwitterion formed from triphenylphosphine and dialkyl azodicarboxylate, has been utilized recently in various heterocyclic constructions. This Focus Review summarizes the potential utility of azodicarboxylates in various carbon-nitrogen bond-forming reactions.

Reaction of dimethoxycarbene-DMAD zwitterion with 1,2-diones and anhydrides: a novel synthesis of highly substituted dihydrofurans and spirodihydrofurans.

The zwitterion formed by the reaction of dimethoxycarbene and DMAD adds efficiently to one of the carbonyl groups of 1,2-dicarbonyl compounds and anhydrides to generate dihydrofurans and spirodihydrofurans in good yields. In many cases, the carbene inserts into the C-C bond of the dione to yield masked vicinal tricarbonyl systems.