Exploiting the divergent reactivity of α-isocyanoacetate: multicomponent synthesis of 5-alkoxyoxazoles and related heterocycles

Mechanochemical IMCR and IMCR-post transformation domino strategies: towards the sustainable DOS of dipeptide-like and heterocyclic peptidomimetics

A facile, rapid, sustainable one-pot Diversity Oriented Synthesis of peptidomimetics via mechanochemical IMCR-based domino strategies.

Microwave-Assisted One Pot Three-Component Synthesis of Novel Bioactive Thiazolyl-Pyridazinediones as Potential Antimicrobial Agents against Antibiotic-Resistant Bacteria

Pyridazine and thiazole derivatives have various biological activities such as antimicrobial, analgesic, anticancer, anticonvulsant, antitubercular and other anticipated biological properties. Chitosan can be used as heterogeneous phase transfer basic biocatalyst in heterocyclic syntheses. Novel 1-thiazolyl-pyridazinedione derivatives were prepared via multicomponent synthesis under microwave irradiation as ecofriendly energy source and using the eco-friendly naturally occurring chitosan basic catalyst with high/efficient yields and short reaction time. All the prepared compounds were fully characterized by spectroscopic methods, and their in vitro biological activities were investigated. The obtained results were compared with those of standard antibacterial/antifungal agents. DFT calculations and molecular docking studies were used to investigate the electronic properties and molecular interactions with specific microbial receptors.

Still Unconquered: Enantioselective Passerini and Ugi Multicomponent Reactions

The Passerini three-component (P-3CR) and the Ugi four-component (U-4CR) are two of the most prominent isocyanide-based multicomponent reactions (IMCRs). The P-3CR transforms isocyanides, aldehydes (ketones), and carboxylic acids to α-acyloxy carboxamides, while the U-4CR converts isocyanides, aldehydes (ketones), amines, and carboxylic acids to α-acetamido carboxamides. Conversion of the high energy formal divalent isocyano carbon into a tetravalent amide carbonyl carbon provides the driving force for these reactions. While the prototypical P-3CR and U-4CR provide linear adducts, many heterocycles and macrocycles are now readily synthesized by modifying these truly versatile reactions. As one stereocenter is generated by the nucleophilic addition of the isocyanide to the carbonyl and imine functions, the search for enantioselective versions of these reactions has become a much sought after goal among synthetic chemists. This seemingly trivial endeavor turns out to be extremely difficult to achieve, in sharp contrast to the remarkable progress documented in the field of asymmetric synthesis in general and catalytic enantioselective nucleophilic addition to C═X bond in particular. Since Denmark's first report in 2003 on the catalytic enantioselective Passerini two-component reaction of isocyanides with aldehydes, several Lewis acid (LA) and Brønsted acid-catalyzed enantioselective protocols have been developed. However, it is fair to say that truly catalytic enantioselective P-3CR and U-4CR with wide application scope remain elusive. In this Account, we summarize the progress recorded in this field over the past 15 years. We entered the field by investigating the enantioselective reaction of α-isocyanoacetamides with aldehydes and imines, which was previously developed in our lab for the synthesis of functionalized 5-aminooxazoles. Our initial experimental results, in conjunction with Dömling's and Schreiber's earlier findings, prompted us to assume that the low turnover number in LA-catalyzed asymmetric IMCRs is a main hurdle for enantioselectivity. We speculated that the LA incapable of forming chelates would be the catalyst of choice for enantioselectivity, the rational being that the P-3CR and the U-4CR afforded bidentate intermediates (α-hydroxy imidates, α-amino imidates) and products (α-acyloxy carboxamides, α-acetamido carboxamides) from nonchelating inputs. Therefore, the transfer of catalyst from these chelating intermediates or products to the monocoordinating starting materials would be difficult, hence the problem with catalyst turnover. This working hypothesis turned out to be a valuable guide that allowed us to develop Al-salen and Al-phosphate-catalyzed enantioselective P-3CR and enantioselective construction of chiral heterocycles such as oxazoles and tetrazoles. Nevertheless, all our attempts to apply these LA catalysts to the Ugi reaction failed. Indeed, to date, no reports on the successful LA-catalyzed asymmetric Ugi-type reactions exist in the literature. However, significant progress has been made in recent years employing organocatalysts. We developed a chiral phosphoric acid (CPA)-catalyzed enantioselective three-component synthesis of 2-(1-aminoalkyl)-5-aminooxazoles, a four-component synthesis of epoxy-tetrahydropyrrolo[3,4- b]pyridin-5-ones and a Ugi four-center, three-component reaction of isocyanides, anilines, and 2-formylbenzoic acids for the synthesis of isoindolinones. Other groups have found that chiral dicarboxylic acid and BOROX are effective catalysts for truncated Ugi three-component reactions.

To each his own: isonitriles for all flavors. Functionalized isocyanides as valuable tools in organic synthesis

The term functionalized isocyanides refers to all those isocyanides in which a neighbouring functional group can finely tune the reactivity of the isocyano group or can be exploited in post-functionalization processes. In this manuscript, we have reviewed all the isocyanides in which the pendant functional group causes either deviation from or reinforces the normal reactivity of the isocyano group and categorized them to highlight their common features and differences. An analysis of their synthetic potential and the possible unexplored directions for future research studies is also addressed.

Copper-catalyzed cyclization of 2-cyanobenzaldehydes and 2-isocyanoacetates: an efficient strategy for the synthesis of substituted 1-aminoisoquinolines

An efficient strategy for the synthesis of substituted 1-aminoisoquinoline has been developed.

The iridium-catalysed reductive coupling reaction of tertiary lactams/amides with isocyanoacetates

A catalytic reductive addition of isocyanoacetates to tertiary lactams/amides has been developed. This one-pot procedure involves Ir-catalysed partial reduction of lactams/amides and sequential chemoselective addition of isocyanide group in isocyanoacetates and produces 5-methoxyoxazoles in moderate to excellent yields.

Microwave-assisted one pot three-component synthesis of some novel pyrazole scaffolds as potent anticancer agents

Background

Pyrazoles, thiazoles and 1,3,4-thiadiazoles have been reported to possess various pharmacological activities.

Results

An efficient and a novel approach for the synthesis of some novel pyrazole based-azoles are described via multi-component reaction under controlled microwave heating conditions. The structures of the synthesized compounds were assigned on the basis of elemental analysis, IR, ¹H NMR and mass spectral data. All the synthesized compounds were tested for in vitro activities against two antitumor cell lines, human lung cancer and human hepatocellular carcinoma compared with the employed standard antitumor drug (cisplatin).

Conclusions

All the newly synthesized compounds were evaluated for their anticancer activity against human lung cancer and human hepatocellular carcinoma cell lines using MTT assay. The results obtained exploring the high potency of six of the tested compounds compared with cisplatin. Graphical abstract

Three-component reactions of isocyanoacetates, amines and 3-formylchromones initiated by an unexpected aza-Michael addition

We present herein a new mode of three-component reactions between isocyanoacetates, amines and 3-formylchromones. Mechanistic and DFT studies reveals that this Ag-catalyzed process is initiated by a facile aza-Michael addition.

Dioxazoles, a new mild nitrene transfer reagent in gold catalysis: highly efficient synthesis of functionalized oxazoles

A gold-catalyzed regioselective [3+2] cycloaddition of ynamides with 1,4,2-dioxazoles was developed and offers a novel approach to obtain highly functionalized oxazoles under mild reaction conditions. 1,4,2-Dioxazole was found to act as an efficient N-acyl nitrene equivalent to trigger a facile generation of α-imino gold-carbene intermediate through the elimination of a ketone.

Synthesis of annulated pyridines as inhibitors of aldosterone synthase (CYP11B2)

A series of potent and selective aldosterone synthase (CYP11B2) inhibitors were prepared in one step through an intermolecular Kondrat'eva reaction.

Catalytic asymmetric conjugate addition of isocyanoacetate to (Z)-3-substituted-2-(4-pyridyl)-acrylonitrile, a reactive class of Michael acceptor

Un-substituted isocyanoacetate ethyl ester reacted with Michael acceptors 1a–m under the catalysis of Cinchona based quaternary ammonium salts providing imines 4a–m as a single diastereoisomer and in up to 94% ees.

Novel 4-heteroaryl-antipyrines as DPP-IV inhibitors

Type 2 diabetes mellitus is a vast growing progressive disease that almost affects one person among every twelve globally. Regardless the availability of wide variety of oral hypoglycemics, only one-third of patients achieves proper glycemic control. With the advantage of the low risk of hypoglycemia, DPP-IV attracted the attention of medicinal chemists as a new target for oral hypoglycemics. In this report, a lead compound 1, with antipyrine scaffold, was obtained, and its binding mode was calculated. Several derivatives with bridged nitrogenous heterocycles have been synthesized via multicomponent reaction under controlled microwave heating conditions. The antidiabetic activity versus DPP-IV protein was evaluated and compared with sitagliptin. Compounds with smaller- or medium-sized nitrogenous bridges were comparable with sitagliptin in terms of DPP-IV inhibitory activity, potentially via targeting Glu203 and Glu204. The oral hypoglycemic activities of compounds with submicromolar IC50 values were further evaluated using diabetic mouse model.

Catalytic enantioselective addition of isocyanoacetate to 3-methyl-4-nitro-5-styrylisoxazoles under phase transfer catalysis conditions

The reaction between 3-methyl-4-nitro-5-styrylisoxazoles and ethyl isocyanoacetate proceeded under PTC to give enantioenriched monoadducts in high ee (up to 99%).

Facile synthesis of 1H-imidazo[1,2-b]pyrazoles via a sequential one-pot synthetic approach

5-Aminopyrazole-4-carbonitrile and ethyl 5-aminopyrazole-4-carboxylate, as potential trifunctional building blocks are introduced in a facile, chemo- and regioselective multicomponent assembly of imidazo[1,2-b]pyrazoles via the Groebke–Blackburn–Bienaymé reaction (GBB reaction). Besides the synthetic elaboration of a green-compatible isocyanide-based access in three-component mode, we describe an operationally simple, one-pot two-step GBB protocol for the rapid construction of a 46 membered imidazo[1,2-b]pyrazole library with yields up to 83%.

Palladium-catalyzed imidoylative cyclization of α-isocyanoacetamides: efficient access to C2-diversified oxazoles

A novel procedure for the synthesis of C2-diversified oxazoles, through palladium-catalyzed imidoylative cyclization of α-isocyanoacetamides with aryl, vinyl, alkynyl halides, or triflates, was developed. Migratory insertion of isocyanide into a Csp3-palladium(II) intermediate in a cascade process was also realized, generating alkyl-substituted oxazoles. Therefore, oxazoles functionalized at the C2 position with sp, sp(2), and sp(3) hybridized carbon atoms are accessible by applying this method.

Triple role of phenylselenonyl group enabled a one-pot synthesis of 1,3-oxazinan-2-ones from α-isocyanoacetates, phenyl vinyl selenones, and water

Reaction of α-substituted α-isocyanoacetates with phenyl vinyl selenones in the presence of a catalytic amount of base (DBU or Et3N, 0.05-0.1 equiv) followed by addition of p-toluenesulfonic acid (PTSA, 0.1-0.2 equiv) afforded 4,4,5-trisubstituted 1,3-oxazinan-2-ones in good to excellent yields. Enantiomerically enriched heterocycles can also be prepared using a Cinchona alkaloid-derived bifunctional organocatalyst for the Michael addition step. The phenylselenonyl group served as an activator for the Michael addition, a leaving group and a latent oxidant in this integrated reaction sequence.

Synthesis of 4-substituted imino-4H-benzo[d][1,3] thiazin-2-amines via palladium-catalysed isocyanide insertion in 2-bromophenylthioureas

The palladium-catalysed isocyanide insertion in 2-bromophenylthioureas leads to the formation of 4-substituted imino-4H-benzo[d][1,3]thiazin-2-amines via C–S cross coupling reaction of the intermediate imidoylpalladium species.

Pseudo-four component synthesis of mono- and di-benzylated-1,2,3-triazoles derived from aniline

The pseudo-four component click synthesis of dibenzylated 1,2,3-triazoles derived from aniline is reported. The cycloaddition of sodium azide to N-(prop-2-ynyl)-benzenamine (I) in the presence of equimolar amounts of p-substituted benzyl derivatives, yields a mixture of mono- and dibenzylated 1,2,3-triazoles. When two equivalents of the benzyl derivative are added to the multicomponent reaction, the selective preparation of the dibenzylated compounds is achieved. The reactivity of the aniline N-H bond in monobenzylated 1,2,3-triazoles was tested by treatment with one equivalent of a p-substituted benzyl chloride at 40 °C, rendering the dibenzylated derivatives quantitatively.

The Kondrat'eva reaction in flow: direct access to annulated pyridines

A continuous flow inverse-electron-demand Kondrat'eva reaction has been developed that provides direct access to cycloalka[c]pyridines from unactivated oxazoles and cycloalkenes. Annulated pyridines obtained by this one-step process are valuable scaffolds for medicinal chemistry.