Copper-Catalyzed Synthesis of Polysubstituted Pyrroles through [3+1+1] Cycloaddition Reaction of Nitrones and Isocyanides

Synthesis of β-Carbonyl α-Iminoamides by Double Insertion of Isocyanides into Aldehydes

An unprecedented trimethylsilyl trifluoromethanesulfonate (TMSOTf)-promoted selective double insertion of isocyanides into aldehydes was developed, providing an efficient protocol for synthetically challenging β-carbonyl α-iminoamides. The given approach is applicable for a diverse selection of readily accessible aldehydes, along with isocyanides serving as essential precursors for "amide" and "imine" scaffolds. The versatile transformations of the given products were demonstrated, and the pivotal intermediates for the plausible mechanism were identified.

Synthesis of Bridged Cycloisoxazoline Scaffolds via Rhodium-Catalyzed Coupling of Nitrones with Cyclic Carbonate

Bridged isoxazolidines were synthesized via Rh(III)-catalyzed C-H allylation of α-aryl nitrones with 5-methylene-1,3-dioxan-2-one. The nitrone group serves as a directing group and 1,3-dipole in the C-H activation/[3 + 2] cycloaddition cascade, exhibiting excellent chemo- and stereoselectivity along with good functional group compatibility. The resulting skeletal structure was conveniently modified to produce a range of important chemical frameworks, and the protocol was applied to biologically active molecules.

Stereo- and Regiospecific SN2' Reaction of MBH Adducts with Isocyanoacetates: en Route to Transition-Metal-Free α-Allylation of Isocyanoacetates

Herein, we report that under mild and transition-metal-free conditions an unprecedented and practical S_N2' reaction of Morita-Baylis-Hillman adducts with isocyanoacetates takes place in a stereo- and regiospecific manner. This reaction which tolerates a wide variety of functionalities delivers transformable α-allylated isocyanoacetates in high efficiencies. Preliminary studies on the asymmetric version of this reaction indicate that ZnEt₂/chiral amino alcohol combinations are an asymmetric catalytic system for this transformation, giving an enantioenriched α-allylated isocyanoacetate with a chiral quaternary carbon in a high yield.

Triple-Consecutive Isocyanide Insertions with Aldehydes: Synthesis of 4-Cyanooxazoles

An efficient TMSOTf-promoted selective triple consecutive insertions of tert-butyl isocyanide into aldehydes has been developed, affording pharmacological interesting 4-cyanooxazoles in high yields in a one pot manner. The given method encompasses a wide range of substrates with tert-butyl isocyanide serving as sources of critical "CN" and "C-N═C" moieties. The versatile transformations of the resulting 4-cyanooxazoles were demonstrated. The key reaction intermediates for plausible mechanisms were determined.

Diboron reagents in the deoxygenation of nitrones

B₂nep₂ efficiently promotes the N-O cleavage of nitrones to form imines in very high yields via a simple, efficient, sustainable, functional group tolerant and scalable protocol. The reaction occurs in the absence of additives through a concerted mechanism. We demonstrated that DMPO and TEMPO, typically used as radical traps, are also deoxygenated by diboron reagents, which demonstrates their limitation as mechanistic probes.

Multicomponent Reaction of Isocyanide, Ditelluride, and Mn(III) Carboxylate: Synthesis of N-Acyl Tellurocarbamate

A multicomponent reaction of isocyanides, ditellurides and manganese(III) carboxylates under mild reaction conditions leads to the synthesis of various N-acyl tellurocarbamates. This method demonstrates good functional tolerance and broad substrate scope and, as a result, is especially suitable for the postfunctionalization of complicated molecules such as drugs. The given method can be further extended to the synthesis of selenocarbamates.

2,2,2-Trifluoroacetaldehyde O-(Aryl)oxime: A Precursor of Trifluoroacetonitrile

The preparation of 2,2,2-trifluoroacetaldehyde O-(aryl)oxime, a previously inaccessible precursor of trifluoroacetonitrile, via reaction of hydroxylamine and trifluoroacetaldehyde hydrate is reported. This precursor released CF₃CN in quantitative yield under mildly basic conditions. The precursor was successfully used in the synthesis of trifluoromethylated oxadiazoles. The facile, cost-effective, scalable, and recyclable procedure makes these trifluoroacetonitrile precursors generally applicable.

Copper-catalyzed C-H/N-H annulation of enaminones and alkynyl esters for densely substituted pyrrole synthesis

Herein, the copper-catalyzed annulation of enaminones with alkynyl esters for the facile synthesis of different pyrroles with a 2,3,4,5-tetrasubstituted structure has been developed. With Cu(OAc)₂ as the only catalyst, the tunable synthesis of 2-vinyl and 2,3-dicarboxyl-functionalized pyrroles has been achieved by using terminal and internal alkynyl esters, respectively. The synthesis of 2-vinyl pyrroles represents the first example accessing 2-vinyl substituted pyrroles via direct cascade reactions involving vinylation and pyrrole ring formation.

I2-Mediated [3 + 2] annulation of methyl-azaarenes with alkyl 2-isocyanoacetates or amino acid ester hydrochlorides: selective synthesis of iodine-functionalized and non-iodine-functionalized fused imidazoles

An I2-mediated [3 + 2] annulation of methyl-azaarenes with alkyl 2-isocyanoacetates or amino acid ester hydrochlorides has been demonstrated. This strategy involves the C≡N cleavage of isocyanides and can selectively...

Synthesis of Poly-Substituted Pyridines via Noble-Metal-Free Cycloaddition of Ketones and Imines

An eco-friendly and noble-metal-free formal [4+2] cycloaddition reaction was developed for the efficient synthesis of biologically interesting poly-substituted pyridines from easily available ketones and imines, whereby two sequential C-C bonds are formed. The given approach features a unique synthetic strategy of imines and ketones with wide substrate scope, good functional group tolerance, mild conditions and operational simplicity, which represents a more direct pathway to synthesize poly-substituted pyridines than traditional methods.

Cascade Reaction of Tryptamine-Derived Isocyanides with Nitrile Oxides: Construction of Oxazine Fused-Spiroindoline Derivatives

A one-step cascade reaction of tryptamine-derived isocyanides with in situ generated nitrile oxides for the synthesis of fused spiroindolines was described. The desired products could be efficiently synthesized in moderate to good yields (42-87%). The protocol features mild conditions, wide substrate scope, and high efficiency.

Mild and Efficient Copper-Catalyzed Synthesis of Trisubstituted Pyrroles

A sustainable and time economic approach has been developed for the synthesis of polysubstituted pyrroles using copper iodide as a catalyst. The reaction proceeded through imine formation followed by cyclization with alkyne-Cu intermediate, which was supported by control experiments studies. The newly formed substituted pyrroles were obtained in excellent yields with high regioselectivity under mild conditions.

Synthesis of strained 1,2-diazetidines via [3 + 1] cycloaddition of C,N-cyclic azomethine imines with isocyanides and synthetic derivation

Strained diazetidines are assembled simply from 1,3-dipolar cycloaddition of isocyanides and C,N-cyclic azomethine imines, and their diversified transformations are presented.

Transition-metal-free and facile synthesis of 3-alkynylpyrrole-2,4-dicarboxylates from methylene isocyanides and propiolaldehyde

A transition-metal-free, facile and efficient method for the synthesis of 3-alkynylpyrrole-2,4-dicarboxylates was developed.

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.

Synthesis of 2,3-Disubstituted 4-Ethoxycarbonyl-β-carbolin-1-ones: Application to the Synthesis of SL651498 and Its Analogue

Synthesis of 2,3-disubstituted 4-ethoxycarbonyl-β-carbolin-1-ones is developed using palladium-catalyzed intramolecular amination of 3-amino-4-(2-bromophenyl)-2-pyridones prepared by the conjugate addition reaction of diethyl 2-aminomalonate to alkynyl imines. The method was applied to the total syntheses of SL651498 exhibiting anxiolytic activity and its analogue.

Silver-Assisted [3 + 2] Annulation of Nitrones with Isocyanides: Synthesis of 2,3,4-Trisubstituted 1,2,4-Oxadiazolidin-5-ones

A silver-assisted method for [3 + 2] annulation of nitrones with isocyanides has been developed. The developed protocol allows access to a variety of 2,3,4-trisubstituted 1,2,4-oxadiazolidin-5-one derivatives as single diastereomers in good to excellent yields using silver oxide as the catalyst and molecular oxygen as the terminal oxidant. A plausible mechanism involving a nucleophilic addition/cyclization/protodeargentation/oxidation pathway is proposed on the basis of experimental results.

Synthesis of Sulfamate-Fused 2-Aminopyrroles via an Isocyanide-Based Three Component [1+2+2] Annulation

An efficient preparation of sulfamate-fused 2-aminopyrroles was achieved through an isocyanide-based three-component [1+2+2] annulation of isocyanides, dialkyl acetylenedicarboxylates, and sulfamate-derived cyclic imines in good to excellent yields (up to 99 %). This reaction proceeds smoothly without any activation or modification of substances under neutral and metal-free conditions. The reaction could also be conveniently performed on a gram scale.

Synthesis of 2,3,4-trisubstituted pyrrole derivatives via [3 + 2] cyclization of activated methylene isocyanides with 4-(arylidene)-2-substituted oxazol-5(4H)-ones

An efficient base-catalyzed [3 + 2] cyclization between isocyanides and 4-(arylidene)-2-substituted oxazol-5(4H)-ones has been successfully developed to form 2,3,4-trisubstituted and 2,2,3,4-tetrasubstituted pyrrole derivatives.

Gold-catalyzed generation of azafulvenium from an enyne sulfonamide: rapid access to fully substituted pyrroles

A one-pot gold-catalyzed protocol for the synthesis of fully substituted pyrroles from enyne sulfonamides has been developed.

Cu-Catalyzed [3 + 3] Cycloaddition of Isocyanoacetates with Aziridines and Stereoselective Access to α,γ-Diamino Acids

We report herein an efficient Cu-catalyzed formal [3 + 3] cycloaddition of isocyanoacetates with readily available aziridines of different substitution patterns, which provides a practical access to valuable 1,4,5,6-tetrahydropyrimidine derivatives. In particular, the use of enantiopure aziridines delivers disubstituted tetrahydropyrimidines bearing a 1,3-diamino unit in good yields as a single stereoisomer (>20:1 dr, > 99% ee). The heterocyclic products can also be easily converted to synthetically useful amino alcohol derivatives or α,γ-diamino acids.