A one-step route to azomethine ylides via chloroiminium salts

A new, one-step procedure for the generation of azomethine ylides, 4 and 20, via chloroiminium salts, 3 and 19, is reported. The generation of the azomethine ylides was confirmed by their trapping with dimethyl acetylenedicarboxylate (DMAD) which, upon spontaneous 1,4-dehydrochlorination, gave the corresponding pyrroles 17 and 21.     

Synthesis of pyrrolo[3,4-c]quinolines by 1,5-electrocyclisation of non-stabilised azomethine ylides

A new route to the pyrrolo[3,4-c]quinoline ring system has been developed via the 1,5-dipolar electrocyclisation reactions of azomethine ylides derived from easily available 3-formylquinoline derivatives. The intermediacy of azomethine ylides was shown by the trapping of the proposed dipoles with N-phenylmaleimide.     

A facile synthesis of novel dispiroheterocycles through solvent-free microwave-assisted [3+2] cycloaddition of azomethine ylides

A comparative study of the synthesis of novel dispiro pyrrolo/pyrrolizidino ring systems by the cycloaddition of azomethine ylides generated by a decarboxylative route from sarcosine/proline and isatin with the dipolarophile 9-arylidine-fluorene using four different methodologies is described. A solvent-free microwave-assisted approach gave products with the highest yields in a short time. Additionally, our solvent-free approach allowed the use of 4-N,N-dimethylaminobenzaldehyde, which failed to yield the desired cycloadducts under conventional approaches.     

A facile synthesis of ferrocene grafted N-methyl-spiropyrrolidines through 1,3-dipolar cycloaddition of azomethine ylides

One-pot synthesis of novel ferrocene grafted N-methyl-spiropyrrolidines has been accomplished in good yields through a facile 1,3-dipolar cycloaddition reaction of various azomethine ylide derived from ninhydrin and sarcosine with various ferrocene derivatives as dipolarophile. The regiochemical and stereochemical outcome of the cycloaddition reaction is ascertained by X-ray crystallographic studies of one of the cycloadducts.     

Synthesis of glucosylspiro-oxindole derivatives via one-pot three-component cycloaddition of azomethine ylides

Highly regio- and stereoselective synthesis of glucosylspiro-oxindole/acenaphthenone derivatives was accomplished through 1,3-dipolar cycloaddition (1,3-DC) reaction. The glucosyl α,β-unsaturated-7,3-lactone (a sugar lactone) derived from d-glucose was used as a chiral dipolarophile in 1,3-DC reaction for the first time. The azomethine ylides generated from sarcosine/l-proline/thiazolidine-4-carboxylic acid/piperidine-2-carboxylic acid with isatin and acenaphthoquinone were trapped by the sugar lactone to give a series of glucosylspiro-pyrrolidine derivatives in good yields.     

A facile tandem carbene-ylide route to 2-fluoropyrrole derivatives

2-Fluoropyrroles were synthesised via 1,3-dipolar cycloaddition of iminiodifluoromethanides derived from corresponding imines and difluorocarbene to dimethyl acetylenedicarboxylate.     

1,3-Dipolar cycloadditions of nonstabilized azomethine ylides to planar chalcones via regio- and stereoselective route: A three-component strategy

Simple and efficient strategies toward the synthesis of trisubstituted pyrrolizidines and disubstituted oxazolidine systems by 1,3-dipolar cycloaddition reactions using arylaldehydes and α-amino acids have been developed, followed by a one-pot, three-component strategy. Electron-deficient dipolarophiles, chalcones, were reacted with nonstabilized azomethine ylides derived from arylaldehyde and L-proline in dry dimethyl formamide, leading to substituted pyrrolizidines. The route to substituted oxazolidines involved cycloaddition to the C?O bond of a second molecule of the aldehyde. The structures and stereochemistry of the cycloadducts were established by infrared (IR), NMR spectroscopy, and single-crystal x-ray crystallographic analyses. Condensed Fukui functions and local electrophilicity indices have been computed to characterize the reactive sites and predict the preferred interactions of azomethine ylides to planar chalcones. The softness-matching indices have been evaluated to determine the regioselectivity of the cycloaddition reactions. The theoretical predictions were found to be in complete agreement with the experimental results, implying that the density functional theory (DFT)-based reactivity indices correctly predict the regioselectivities of 1,3-dipolar cycloadditions of azomethine ylides to planar chalcones. The frontier molecular orbital (FMO) energies, electronic chemical potentials, chemical hardness, chemical softness, and global electrophilicity indices of azomethine ylides have been calculated at the DFT/B3LYP/6-31 + G (d, p) level of theory.     

On the Most Powerful Chemical Traps for Bis(methoxycarbonyl)carbene (=2‐Methoxy‐1‐(methoxycarbonyl)‐2‐oxoethylidene)

The efficiency and validity of different chemical substrates for trapping bis(methoxycarbonyl)carbene (=2‐methoxy‐1‐(methoxycarbonyl)‐2‐oxoethylidene; 1 ) is dependent on the conditions of carbene generation. On conventional photolysis of dimethyldiazomalonate (=2‐diazopropanedioic acid dimethyl ester; 2 ) by long‐wave UV light (through a Pyrex filter, λ>290 nm), the most powerful trap for carbene 1 in the series of substrates Me₂S, MeOH, cyclohexane, and pyridine is Me₂S (with an efficiency ratio of ca. 6 : 4 : 2 : 1, resp.). When short‐wave decomposition of diazomalonate 2 is employed (through a quartz filter, λ>210 nm), more reliable and useful chemical traps for bis(methoxycarbonyl)carbene ( 1 ) are pyridine and cyclohexane, whose adducts with 1 are rather stable under short‐wave‐irradiation conditions. Application of alcohols for the trapping of 1 proves to be preferential when simultaneous monitoring of carbene and oxoketene formation during photolysis is necessary.     

An expedient synthesis of ferrocene grafted spirooxindolopyrrolizidines via [3+2]-cycloaddition of azomethine ylides

A facile and rapid one-pot synthesis of ferrocene bearing novel spiropyrrolizidines has been accomplished by [3+2]-cycloaddition reaction of various azomethine ylides derived from isatin/5,7-dibromoisatin and l-proline with various ferrocene derivatives as dipolarophile in good yield. The protocol is general and applicable to a wide variety of ferrocenyl derived dipolarophiles. Effect of various solvents on [3+2]-dipolar cycloaddition reaction is also studied.     

1,3-Dipolar cycloaddition reaction of bipyridinium ylides with the propynamido-β-cyclodextrin. A regiospecific synthesis of a new class of fluorescent β-cyclodextrins

The 1,3-dipolar cycloaddition reaction of bipyridinium ylides with the electron deficient propynamido-β-cyclodextrin was studied. This reaction resulted in the regiospecific formation of a new class of fluorescent β-cyclodextrins. The new fluorophore systems were characterized spectroscopically by their absorption and emission maxima and their quantum yields.     

A facile route to ruthenium–carbene complexes and their application in furfural hydrogenation

A number of new N‐heterocyclic carbene (NHC) ligands were synthesized via a multicomponent reaction, wherein an aldehyde or ketone, a primary amine and an α‐acidic isocyanide were reacted, giving the corresponding 2H‐2‐imidazolines. These were easily alkylated with an alkyl halide at position N‐3, yielding the final NHC precursors, that were then complexed with Ru in situ. The resulting complexes are shown to be active and selective catalysts for the transfer hydrogenation of furfural to furfurol, using isopropanol as the hydrogen source. Importantly, the carbene ligand remains coordinated to the ruthenium center throughout the reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

An easy access to novel steroidal dispiropyrrolidines through 1,3-dipolar cycloaddition of azomethine ylides

A facile one-pot synthesis of novel steroidal dispiropyrrolidines has been accomplished by 1,3-dipolar cycloaddition reaction of various azomethine ylides derived from isatin/acenaphthenequinone/ninhydrin and sarcosine with various estrone derivatives as dipolarophiles, in good yield. The effect of various solvents on the 1,3-dipolar cycloaddition reaction are also studied.     

Thiourea-catalyzed asymmetric formal [3+2] cycloaddition of azomethine ylides with nitroolefins

A chiral thiourea catalyst possessing an amine function catalyzes an asymmetric [3+2] cycloaddition of azomethine ylides to nitroolefins to provide highly functionalized pyrrolidines with high diastereo- and enantioselectivities (up to 98:1:1 dr, 92% ee). The reaction proceeds in a stepwise manner consisting of Michael addition and subsequent intramolecular aza-Henry reaction. Both reactions are promoted by the thiourea catalyst, and the reaction rate of the latter step is efficiently enhanced by the addition of 2,2,2-trifluoroethanol.     

Nucleophilic phosphine-catalyzed [3+2] cycloaddition of allenes with N-(thio)phosphoryl imines and acidic methanolysis of adducts N-(thio)phosphoryl 3-pyrrolines: a facile synthesis of free amine 3-pyrrolines

In this report, the dipolarophile imines with easily removable activating group O,O-diethyl(thio)phosphoryl have been investigated in the nucleophilic phosphine-catalyzed [3+2] cycloaddition reaction of electron-deficient allenes. Under the catalysis of a tertiary phosphine, N-(thio)phosphorylimines readily undergo the [3+2] cycloaddition reaction with ethyl 2,3-butadienoate or ethyl 2,3-pentadienoate, affording the corresponding N-(thio)phosphoryl 3-pyrrolines in moderate to high yields with good diastereoselectivity. Removal of the (thio)phosphoryl group from the adducts has been successfully achieved via the acidic methanolysis of the P-N bond, giving the free amine 3-pyrrolines in fair to good yields without severe aromatization. Thus, a facile synthesis of N-unsubstituted 3-pyrrolines is established from the phosphine-catalyzed [3+2] cycloaddition reaction of allenes with imines.     

A facile synthetic route to new pyrazoloisoindolones

A facile method for the synthesis of new pyrazoloisoindolones via a Suzuki cross-coupling reaction using a pyrazolylboronic ester is described.     

1,5-Electrocyclisation of azomethine ylides leading to pyrrolo[2,1-a]isoquinolines—concise construction of the lamellarin skeleton

A new, general route to the 1,2-diaryl-substituted pyrrolo[2,1-a]isoquinolines has been developed via the 1,5-dipolar electrocyclisation reactions of azomethine ylides derived from readily available stilbenic acid derivatives. This method was applied to the concise construction of a lamellarin skeleton.     

Nucleophilic properties of a nonstabilized azomethine ylide derived from sarcosine and cyclohexanone. A novel domino reaction leading to substituted 4-aryl-2-pyrrolidones

A nonstabilized asymmetric azomethine ylide derived from sarcosine and cyclohexanone reacts with 3-substituted coumarins and ethyl benzylidene malonate to give 4-aryl-2-pyrrolidones in moderate yields, and the adducts of classical 1,3-dipolar cycloadditions as the minor products. The main reaction proceeds via a domino process, starting with 1,4-nucleophilic addition to the conjugated double bond, and represents the first example of the nucleophilic properties of a nonstabilized azomethine ylide.     

A new process of multicomponent Povarov reaction–aerobic dehydrogenation: synthesis of polysubstituted quinolines

A new domino process of three-component Povarov reaction and aerobic dehydrogenation was developed toward the synthesis of polysubstituted quinolines. 2,4-Disubstituted-8-nitroquinolines, which are important precursors for the synthesis of antimalarial primaquine drug-like molecules, were prepared conveniently by this method in moderate to good yields. Brönsted acid (HClO₄)-modified montmorillonite was found to be a crucial catalyst in promoting the procedure.     

A facile synthesis of indole-furan conjugates via integration of convergent and linear domino reactions

The convergent and linear domino reactions have been first integrated, for the first time, to provide an efficient synthesis of indole-furan conjugates from indoles, methyl ketones, and 1,3-dicarbonyl compounds.     

A new route to the synthesis of isoxazoline derivatives from dihydropyran via cycloaddition reaction in ionic liquid

A new approach to the synthesis and 1,3-dipolar cycloadditions of nitrones has been described from 2,3-dihydro-4H-pyran and various hydroxylamines, with electron-deficient alkynes for the synthesis of isoxazoline derivatives. Significant rate acceleration and improved yields of exclusively exo isoxazolines in 1-butyl-3-methylimidazolium based ionic liquids have been observed. Novel isoxazolines may be used as a precursor for the synthesis of variety of peptides.