ASYMMETRIC 1,3-DIPOLAR CYCLOADDITIONS FOR THE CONSTRUCTION OF ENANTIOMERICALLY PURE HETEROCYCLES. A REVIEW

Stereoselective Asymmetric Syntheses of Molecules with a 4,5-Dihydro-1H-[1,2,4]-Triazoline Core Possessing an Acetylated Carbohydrate Appendage: Crystal Structure, Spectroscopy, and Pharmacology

A new series of chiral 4,5-dihydro-1H-[1,2,4]-triazoline molecules, featuring a β-ᴅ-glucopyranoside appendage, were synthesized via a 1,3-dipolar cycloaddition reaction between various hydrazonyl chlorides and carbohydrate Schiff bases. The isolated enantiopure triazolines (8a-j) were identified through high-resolution mass spectrometry (HRMS) and vibrational spectroscopy. Subsequently, their solution structures were elucidated through NMR spectroscopic techniques. Single-crystal X-ray analysis of derivative 8b provided definitive evidence for the 3-D structure of this compound and revealed important intermolecular forces in the crystal lattice. Moreover, it confirmed the (S)-configuration at the newly generated stereo-center. Selected target compounds were investigated for anti-tumor activity in 60 cancer cell lines, with derivative 8c showing the highest potency, particularly against leukemia. Additionally, substituent-dependent anti-fungal and anti-bacterial behavior was observed.

Reactivity of Rare Earth Metal Alkyl Complexes with Nitriles or Isonitrile: Versatile Ways toward Multiply Functionalized β-Diketiminato, (Iso)indolyl, and Imidazolyl Chelating Rare Earth Metal Complexes

The reactivity of the rare earth metal alkyl complexes LRE(CH2SiMe3)(THF)2 (1RE) [RE = Y (1Y), Yb (1Yb), Lu (1Lu); L = 2,5-[(2-pyrrolyl)CPh2]2(N-methylpyrrole)] with various nitriles and isonitriles has been fully developed. Treatment of the yttrium monoalkyl complex (1Y) with 2 equiv of aromatic nitriles afforded the symmetric trisubstituted β-diketiminato yttrium complexes (2Y(H), 2Y(Me), and 2Y(F)) through successive cyano group insertion into the RE-C bond and 1,3-H shift or the unsymmetric trisubstituted β-diketiminato yttrium complex (3Y) unexpectedly via a 1,3-SiMe3 shift when 4-(trifluoromethyl)benzonitrile was used in this reaction under the same conditions. By treating 1Y with 2 equiv of tolyl acetonitrile, an activation of the sp3 C-H bond occurred to form the corresponding β-aryl keteniminato complexes 4Y(p-tol) and 4Y(m-tol). Remarkably, a heteroleptic cleavage of the CO-CN bond took place in the reaction of 1Y with benzoyl nitrile, affording the unsymmetric trinuclear yttrium complex 5Y bridged by three cyanide groups. Dinuclear ytterbium and lutetium complexes 6Yb and 6Lu containing a functionalized isoindole fragment were synthesized from the reactions of 1 with phthalonitrile by tandem insertion and cyclization. Further studies indicated that the temperature and stoichiometric ratio have a great influence on the reactivity patterns between the reactions of 1RE with benzylisonitrile: two tetrasubstituted β-diketiminato complexes 8 and 9 were obtained at -30 °C, and tetrasubstituted imidazolyl yttrium and lutetium complexes 7 were isolated at elevated temperature, respectively. In addition, the tetrasubstituted β-diketiminato complexes 8 and 9 could be irreversibly converted to the cyclization products 7 by elevating the reaction temperature not only on the NMR scale but also on the preparative scale. Notably, when the phenyl isonitrile instead of benzyl isonitrile was reacted with 1Yb, a 2,3-functionalized indolyl ytterbium complex 10Yb was isolated.

Convenient construction of polycyclic architectures via multicomponent reaction of amino acids, dialkyl but-2-ynedioates and 2-(o-hydroxyarylidene)-1,3-indanediones

Unique polyheterocyclic compounds were efficiently synthesized by cascade reaction of the in situ generation of a special kind of azomethine ylide, 1,3-dipolar cycloaddition and annulation of phenoxide.

Predicting Absolute Rate Constants for Huisgen Reactions of Unsaturated Iminium Ions with Diazoalkanes

The kinetics and stereochemistry of the reactions of iminium ions derived from cinnamaldehydes and MacMillan's imidazolidinones with diphenyldiazomethane and aryldiazomethanes were investigated experimentally and with DFT calculations. The reactions of diphenyldiazomethane with iminium ions derived from MacMillan's second-generation catalysts gave 3-aryl-2,2-diphenylcyclopropanecarbaldehydes with yields >90 % and enantiomeric ratios of ≥90:10. Predominantly 2:1 products were obtained from the corresponding reactions with monoaryldiazomethanes. The measured rate constants are in good agreement with the rate constants derived from the one-center nucleophilicity parameters N and sN of diazomethanes and the one-center electrophilicity parameters E of iminium ions as well as with quantum chemically calculated activation energies.

Quantum chemical studies on the mechanistic aspects of tandem sequential cycloaddition reactions of cyclooctatetraene with ester and nitrones

The mechanisms of the tandem sequential [4 + 2]/[3 + 2] and [3 + 2]/[4 + 2] cycloaddition sequences involving an ester, cyclooctatetraene (COTE), and cyclic and acyclic nitrones for the formation of a diverse range of isoxazolidine derivatives and other synthetic precursors are reported. A thorough exploration of the PES has characterized several regio-, stereo- and enantio-selective mechanistic channels involved in these reactions. A perturbation molecular orbital (PMO) analysis been employed to rationalize the results. It has also been found that the initial electrocyclic ring closure of the COTE is the rate-determining step in the tandem sequential [4 + 2]/[3 + 2] addition sequence. The thermolytic breakdown of the tandem adducts to subsequent monocyclic, bicyclic and tricyclic adducts occurs generally with very high activation barriers making it an inconvenient synthetic approach. The different reactivity of all the three double bonds present in the dipolarophile is reported. Finally, the mechanistic possibilities of [3 + 2]/[4 + 2] addition sequences involving the same reaction components in the case of cyclic and acyclic nitrones are explored extensively. The results suggest a novel and convenient routes for obtaining products of high selectivity with less energetic requirements. In some instances, new cycloadducts hitherto unreported are obtained.

The use of enaminones and enamines as effective synthons for MSA-catalyzed regioselective synthesis of 1,3,4-tri- and 1,3,4,5-tetrasubstituted pyrazoles

In the present work, an efficient regioselective synthesis of 1,3,4-tri- and 1,3,4,5-tetrasubstituted pyrazoles via a methanesulfonic acid (MSA)-catalyzed reaction of hydrazones with enaminones or enamines is reported.

Stereo-, Regio-, and Chemoselective [3 + 2]-Cycloaddition of (2E,4E)-Ethyl 5-(Phenylsulfonyl)penta-2,4-dienoate with Various Azomethine Ylides, Nitrones, and Nitrile Oxides: Synthesis of Pyrrolidine, Isoxazolidine, and Isoxazoline Derivatives and a Computational Study

One-pot chemo-, regio-, and stereoselective synthesis of series of heterocyclic and spiroheterocyclic compounds was accomplished through mono- and bis[3 + 2]-cycloaddition reactions of (2E,4E)-ethyl 5-(phenylsulfonyl)penta-2,4-dienoate as a dipolarophile with azomethine ylides, nitrones, and nitrile oxides in good yields. The structures of the products were established by spectroscopic techniques as well as by single-crystal XRD study, and DFT calculations were performed to further understand the mechanism of this [3 + 2]-cycloaddition reaction.

Molecular diversity of the three-component reaction of α-amino acids, dialkyl acetylenedicarboxylates and N-substituted maleimides

The one-pot three-component reaction of secondary α-amino acids with dialkyl acetylenedicarboxylate and N-substituted maleimides afforded functionalized pyrrolo[3,4-a]pyrrolizines, pyrrolo[3′,4′:3,4]pyrrolo[1,2-c]thiazoles, pyrrolo[3,4-a]indolizines and octahydropyrrolo[3,4-c]pyrroles.

Quickly FeCl3-catalyzed highly chemo- and stereo-selective [3 + 2] dipolar cycloaddition of aziridines with isothiocyanates

A FeCl₃-catalyzed [3 + 2] cycloaddition reaction of aziridine with isothiocyanate was developed.

Convenient synthesis of functionalized spiro[indoline-3,2'-pyrrolizines] or spiro[indoline-3,3'-pyrrolidines] via multicomponent reactions

A general and practical route for the in situ generation of a new type of azomethine ylide and its sequential 1,3-dipolar cycloaddition reaction was successfully established. The three-component reaction of secondary α-amino acids including proline, sarcosine, thiazolidine-4-carboxylic acid with dialkyl acetylenedicarboxylate and 3-methyleneoxindoles in refluxing ethanol afforded the functionalized spiro[indoline-3,2'-pyrrolizines], spiro[indoline-3,3'-pyrrolidines] and spiro[indoline-3,6'-pyrrolo[1,2-c]thiazoles] in good yields and with high diastereoselectivity. Furthermore, similar multicomponent reactions using primary α-amino acids such as glycine, alanine and phenylalanine resulted in the corresponding (spiro[indoline-3,3'-pyrrolidine]-1'-yl)maleates.

A bonding evolution theory study of the mechanism of [3+2] cycloaddition reactions of nitrones with electron-deficient ethylenes

BET study of the mechanism of zw-type [3+2] cycloaddition reactions of nitrones with electron-deficient ethylenes.

A polymer supported ascorbate functionalized task specific ionic liquid: an efficient reusable catalyst for 1,3-dipolar cycloaddition

In situ coalescence of copper on polymer supported ascorbate functionalized task specific ionic liquid, acts as an efficient catalyst for Huisgen 1,3 dipolar cycloaddition.

An efficient synthesis of perhydro[1,2,4]triazolo[1,2-a][1,2,4]triazole-1,5-dithiones catalyzed by TiO2-functionalized nano-Fe3O4 encapsulated-silica particles as a reusable magnetic nanocatalyst

A nano-TiO₂ catalyst on was immobilized on a magnetic SiO₂ support to form a robust and magnetically recoverable Fe₃O₄@SiO₂–TiO₂ catalyst for the synthesis of perhydrotriazolotriazole derivatives by the condensation of aldazines at room temperature.

Non-classical CH⋯O hydrogen-bond determining the regio- and stereoselectivity in the [3 + 2] cycloaddition reaction of (Z)-C-phenyl-N-methylnitrone with dimethyl 2-benzylidenecyclopropane-1,1-dicarboxylate. A topological electron-density study

Formation of a non-classical CH⋯O hydrogen-bond involving the nitrone C–H hydrogen is responsible for the selectivity experimentally found in this non-polar zw-type 32CA reaction.

Regio- and diastereoselectivity of the 1,3-dipolar cycloaddition of α-aryl nitrone with methacrolein. A theoretical investigation

The mechanism, regio- and diastereoselectivity of the 1,3-dipolar cycloaddition of N-iso-propyl,α-(4-trifluoromethyl)-phenyl nitrone with methacrolein yielding the isoxazolidine cycloadduct has been studied at the B3LYP/6-31G(d) level of theory.

Combinatorial synthesis of functionalized spirooxindole-pyrrolidine/pyrrolizidine/pyrrolothiazole derivatives via three-component 1,3-dipolar cycloaddition reactions

A series of diverse polycyclic heterocycles containing spirooxindole, pyridine/thiophene, and pyrrolidine/pyrrolizidine/pyrrolothiazole rings have been synthesized through the 1,3-dipolar cycloaddition of azomethine ylides generated in situ by the condensation of dicarbonyl compounds (isatin or acenaphthenequinone) and secondary amino acids with dipolarophiles. The method is simple and provides diverse and biologically interesting products with excellent yields.

Progress of the synthesis of condensed pyrazole derivatives (from 2010 to mid-2013)

Condensed pyrazole derivatives are important heterocyclic compounds due to their excellent biological activities and have been widely applied in pharmaceutical and agromedical fields. In recent years, numerous condensed pyrazole derivatives have been synthesized and advanced to clinic studies with various biological activities. In this review, we summarized the reported synthesis methods of condensed pyrazole derivatives from 2010 until now. All compounds are divided into three parts according to the rings connected to pyrazole-ring, i.e. [5, 5], [5,F 6], and [5, 7]-condensed pyrazole derivatives. The biological activities and applications in pharmaceutical fields are briefly introduced to offer an orientation for the design and synthesis of condensed pyrazole derivatives with good biological activities.

Synthesis of functionalized dispiro-oxindoles through azomethine ylide dimerization and mechanistic studies to explain the diastereoselectivity

Synthesis of functionalized dispiro-oxindoles via [3 + 3]-cycloaddition of azomethine ylide generated from condensation of isatin and proline is reported. A transition state model for the origin of diastereoselectivity and mechanism of formation of these types of adducts is proposed.