Stereoselective Multiple Bond-Forming Transformations (MBFTs): The Power of 1,2- and 1,3-Dicarbonyl Compounds

Copper-Catalyzed Substrate-Controlled Carbonylative Synthesis of α-Keto Amides and Amides from Alkyl Halides

Controllable production of α-keto amides and amides from the same substrates is an attractive goal in the field of transition-metal-catalyzed (double-)carbonylation. Herein, a novel copper-catalyzed highly selective double carbonylation of alkyl bromides has been developed. Moderate to good yields of α-keto amides were obtained as the only products. In the case of alkyl iodides, double- and mono-carbonylation can be achieved controllably under different conditions.

Orthogonal Catalysis for an Enantioselective Domino Inverse-Electron Demand Diels-Alder/Substitution Reaction

An enantioselective domino process for the synthesis of substituted 1,2‐dihydronaphthalenes has been developed by the combination of chiral amines and a bidentate Lewis acid in an orthogonal catalysis. This new method is based on an inverse electron‐demand Diels−Alder and a subsequent group exchange reaction. An enamine is generated in situ from an aldehyde and a chiral secondary amine catalyst that reacts with phthalazine, activated by the coordination to a bidentate Lewis acid catalyst. The absolute configuration of the product is controlled by chiral information provided by the amine. The formed ortho‐quinodimethane intermediate is then transformed via a group exchange reaction with thiols. The new method shows a broad scope and tolerates a wide range of functional groups with enantiomeric ratios up to 91 : 9. All‐in‐all, this enantioselective synthesis tool provides an easy access to complex 1,2‐dihydronaphthalenes starting from readily available phthalazine, aldehydes and thiols in a combinatorial way.

One-Pot Mechanochemical Synthesis of Mono- and Bis-Indolylquinones via Solvent-Free Multiple Bond-Forming Processes

Bis-indolylquinones are fungal natural products endowed with interesting pharmacological properties. Most of the previously described methodologies in solution for the construction of the bis-indolylquinone framework show disadvantages associated with long reaction times and difficult, waste-generating purifications. A one-pot mechanochemical methodology for the synthesis of indolylquinones was developed, starting from indoles and dihaloquinones in the presence of FeCl₃ or p-TsOH as catalysts and Fetizon's reagent as an oxidant. In contrast to solution chemistry, mechanochemical activation allowed the double addition of indole to a quinone substrate in one pot, leading to symmetrical or non-symmetrical bis-indolylquinones via a domino processes comprising up to six steps. In terms of sustainability, the method has several advantages over the solution protocol, including much shorter reaction times, no external heating, one-pot operation, and the absence of chromatography, leading to a drastically better performance in green metrics and demonstrating the application of several principles of green chemistry, in particular principles 2, 3, and 5.

Diversification of α-ketoamides via transamidation reactions with alkyl and benzyl amines at room temperature

A wide range of N-tosyl α-ketoamides underwent transamidation with various alkyl amines in the absence of a catalyst, base, or additive. On the other hand, transamidation in N-Boc α-ketoamides was achieved in the presence of Cs₂CO₃. The reactions proceeded at room temperature and provided good to excellent yields of transamidation products under the optimized conditions. Broad substrate scope, functional group tolerance and quick conversions are the important features of the developed methodology.

Nitroacetonitrile and Its Synthetic Equivalents

Nitroacetonitrile (NAN) serves as a cyano(nitro)methylating agent facilitating the construction of polyfunctionalized compounds; however, its explosive property is a significant drawback in terms of practical handling. Alkali metal salts of NAN are thermally stable, but their insolubility in organic solvents restricts their use as a synthetic reagents. On the contrary, dipyrrolidinium cyano-aci-nitroacetate is soluble in common organic solvents and thermally stable, allowing for its use as an alternative synthetic equivalent of nitroacetonitrile for the construction of polyfunctionalized frameworks via cyano(nitro)methylation.

How and Why to Investigate Multicomponent Reactions Mechanisms? A Critical Review

We review the most innovative efforts and greatest challenges faced when elucidating multicomponent reactions (MCRs) mechanisms. When compared to traditional reactions, the often two or more concurrent reactions pathways and the greater number of possible intermediates in MCRs turn their mechanistic investigation both a harder and trickier task. The common approaches used to investigate reaction mechanisms are often unable to clarify MCRs mechanisms; hence few but clever approaches are currently used to determine these mechanisms and to depict their key transformations. Their complexity has required most innovative approaches and the use of a number of unique techniques that have shed light over the favored pathway selected from the myriad of alternatives theoretically available for MCRs. This review focuses on the most successful efforts applied by a few leading groups to perform these puzzlingly investigations.

Synthesis of polysubstituted pyrroles via isocyanide-based multicomponent reactions as an efficient synthesis tool

The present review covers all synthetic methods based on isocyanide-based multicomponent reactions for the preparation of polysubstituted pyrroles as the parent cores of many essential drugs, biologically active compounds, and compounds with wide application in materials science.

Stereoselective Four-Component Synthesis of Functionalized 2,3-Dihydro-4-Nitropyrroles

We report a metal-free and stereoselective four-component reaction between α-ketoamides, amines, aromatic aldehydes and β-nitroalkenes or β-pivaloxy-nitroalkanes to obtain 2,3-dihydro-4-nitropyrroles functionalized in every position. The heterocycles accessible using this reaction may have utility in the synthesis of pharmacologically active compounds.

A stereoselective sequential organocascade and multicomponent approach for the preparation of tetrahydropyridines and chimeric derivatives

A stereoselective multicomponent approach leading to a novel class of pentasubstituted tetrahydropyridines is described.

Synergistic catalytic action of vanadia–titania composites towards the microwave-assisted benzoin oxidation

Application of synergistic effects is among the main ways to boost chemical efficiency.

Synthesis of Multifunctionalized 2,3-Dihydro-4-pyridones and 4-Pyridones via the Reaction of Carbamoylated Enaminones with Aldehydes

The novel and effective diastereoselective synthesis of multifunctionalized dihydropyridones, including CF₃-substituted derivatives, has been developed on the basis of the piperidine-promoted domino reaction of carbamoylated enaminones with aldehydes. The products have been prepared in 38-90% yields and can be easily isolated by crystallization. Tautomerism, epimerization, and atropisomerism of dihydropyridones have been studied. The use of the resulting dihydropyridones in the synthesis of 1,2,6-trisubstituted 4-pyridone-3-carboxamides has been demonstrated via oxidative aromatization initiated by iodine.

Normal, Abnormal, and Cascade Wittig Olefinations of α-Oxoketenes

α-Oxoketenes generated in situ by a thermal Wolff rearrangement have been found to participate as 1,2- and 1,4-ambident C-electrophilic/O-nucleophilic reagents towards donor/acceptor carbonyl-stabilized Wittig ylides. This resulted in the very direct and practical syntheses of functionalized allenes by a normal Wittig olefination, 4H-pyran-4-ones by an abnormal Wittig olefination, or 4H-pyranylidenes following a Wittig/abnormal Wittig cascade sequence as a function of the substrates combination employed. Mechanistic experimental and computational studies provided a full rational for these reactivity switches. Some unusual mechanistic features for Lewis acid-free Wittig olefinations were identified in this series such as the involvement of betaine intermediates and some degree of reversibility in the normal Wittig olefination. The abnormal Wittig olefination was fully uncovered.

Multicomponent mechanochemical synthesis

Historically, the use of mechanochemical methods in synthesis has been almost negligible, but their perception by the synthetic community has changed in recent years and they are on their way to becoming mainstream. However, the hybridization of mechanochemical synthesis with methodologies designed to increase synthetic efficiency by allowing the generation of several bonds in a single operation has taken off only recently, but it already constitutes a very promising approach to sustainable chemistry. In this context, we provide in this Perspective a critical summary and discussion of the main known synthetic methods based on mechanochemical multicomponent reactions.

Domino Synthesis of Embelin Derivatives with Antibacterial Activity

A series of dihydropyran embelin derivatives was synthesized through a direct and highly efficient approach based on a domino Knoevenagel intramolecular hetero-Diels-Alder reaction from natural embelin (1), using unsaturated aldehydes in the presence of organocatalysts such as ethylendiamine diacetate or l-proline. The aliphatic aldehydes yielded exclusively trans adducts, while mixtures of trans and cis isomers were found in reactions with aromatic aldehydes, with the cis form always predominating. Some of the compounds obtained were active and selective against Gram-positive bacteria, including multiresistant Staphylococcus aureus clinical isolates.

BF3·OEt2 mediated metal-free one-pot sequential multiple annulation cascade (SMAC) synthesis of complex and diverse tetrahydroisoquinoline fused hybrid molecules

A highly efficient and distinct BF₃·OEt₂ mediated one-pot metal-free sequential multiple annulation cascade (SMAC) protocol for the synthesis of complex and diverse THIQ fused hybrid molecules has been presented.

Ultrasonic-accelerated rapid protocol for the improved synthesis of pyrazoles

A simple, catalyst-free, green synthetic protocol is described for the one-pot synthesis of pyrazoles via multicomponent reaction of aromatic aldehydes, hydrazine monohydrate and ethyl acetoacetate and malononitrile/ammonium acetate in water under ultrasound irradiation. This protocol avoids traditional chromatography and purification steps and it affords highly selective conversion with no byproducts.

Recent advances in the synthesis of pyrroles by multicomponent reactions

Pyrrole is one of the most important one-ring heterocycles. The ready availability of suitably substituted and functionalized pyrrole derivatives is essential for the progress of many branches of science, including biology and materials science. Access to this key heterocycle by multicomponent routes is particularly attractive in terms of synthetic efficiency, and also from the environmental point of view. We update here our previous review on this topic by describing the progress made in this area in the period between mid-2009 and the end of 2013.

The Biginelli reaction under batch and continuous flow conditions: catalysis, mechanism and antitumoral activity

Biginelli scaffolds have been synthesized using two new coordination polymer as catalysts under batch or continuous flow conditions. The mechanism of the reaction and the antitumoral activity of the obtained DHPMs were also evaluated.

Organocatalytic multicomponent synthesis of enantioenriched polycyclic 1,2,3,4-tetrahydropyridines: key substrate selection enabling regio- and stereoselectivities

A completely regioselective and highly enantioselective organocatalytic multicomponent synthesis of 1,2,3,4-tetrahydropyridines is described.

Synergistic Cu–amine catalysis for the enantioselective synthesis of chiral cyclohexenones

An unprecedented utilization of 1,3-acetonedicarboxylic acid as a 1,3-bis-pro-nucleophile and a reactive acetone surrogate in enantioselective catalysis has been reported.

An efficient green protocol for the preparation of acetoacetamides and application of the methodology to a one-pot synthesis of Biginelli dihydropyrimidines. Expansion of dihydropyrimidine topological chemical space

A one pot synthesis of Biginelli dihydropyrimidines. The novel use of the amino acids allows topological diversification of the chemical space.

Diversity oriented synthesis of tri-substituted methane containing aminouracil and hydroxynaphthoquinone/hydroxycoumarin moiety using organocatalysed multicomponent reactions in aqueous medium

One-pot multicomponent reaction of aldehyde, 1,3-dimethyl-6-aminouracil and 2-hydroxy-1,4-naphthoquinone/4-hydroxycoumarin using a bifunctional thiourea-based organocatalyst in aqueous medium has been reported.