1,3-Dipolar cycloaddition reaction of aryl nitrile oxides with alkenes using imidazole and pyridine containing reusable polymeric base catalysts

Cross-linked poly-1-(4-vinylbenzyl)imidazole and cross-linked poly-4-vinylpyridine have been prepared from respective vinyl monomers using different quantities of divinylbenzene as a cross-linker by radical polymerization. The polymeric bases were characterized by FT-IR, TGA, field emission-scanning electron microscopy (FE-SEM), and Brunauer-Emmett-Teller (BET) surface area analysis. Their swelling behavior was also studied. They were used as base catalysts for 1,3-dipolar cycloaddition reaction of aryl nitrile oxides, generated in situ from N-hydroxyimidoyl chloride, with N-phenylmaleimide and ethyl acrylate, to obtain 3-arylisoxazolines. Both the bases gave excellent results. These polymers were reusable, safe to use, and provided good alternative for organic nonreusable bases like pyridine and triethylamine which are hazardous.     

The reaction of 2-nitrosopyridine with nitrile oxides: First synthesis of 1,2,4-triazolo[1,5-a]pyridine 1,3-Di-N-oxides

Reactions of 2-nitrosopyridine with nitrile oxides afford either the novel title compounds or the corresponding 1,2,4-triazolo[1,5-a]pyridine 3-oxides.     

Cycloaddition reaction of phosphonyl nitrile oxides to phosphaacetylene and alkene

Here, we report the cycloaddition reaction of phosphonyl nitrile oxides and the formation of an unexpected 2:1 cycloaddition product. It provides a direct route to triphosphonyl‐substituted dihydroisoxazolyl dihydroisoxazoles and diphosphonyl‐substituted dihydroisoxazolyl dihydroisoxazoles with excellent levels of regiocontrol product. Density functional theory studies of the reactions between nitrile oxides and acrylonitrile are used to propose a possible reaction mechanism. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:95–100, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20518     

2-isoxazoline derivatives—VIII : The reaction of nitrile oxides with tropone

The reaction of nitrile oxides with tropone yields a mixture of at least 8 products, the structures of which are based on spectral and chemical evidence. Both addition of the 1,3-dipole to the carbonyl group and cycloadditions to the CC double bonds system have been observed. Peri-, regio- and stereo-selectivity of the 1,3-dipole cycloaddition are discussed and rationalized on the basis of simple perturbation theory approach.     

Huisgen reaction of nitrile oxides and nitrile imines leading to isoxazoline and pyrazole-4,6-diones

Huisgen reaction of nitrile oxides and nitrile imines generated in situ in the presence of N-benzylmaleimide afforded regiospecifically the corresponding cis-3-aryl-5-benzyl-3a,4,6,6atetrahydro-4H, 6H-pyrrolo[3,4-d]isoxazoline-4,6-diones and cis-3-aryl-5-benzyl-1-(2′,4′-dibromophenyl)-3a, 4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,6-diones in good yield. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 935–939, June, 2006.     

Syntheses based on nitrile oxides. 1. Reaction of aromatic nitrile oxides with N-cyanimides

The reaction of trialkylaminocyanimides with aromatic nitrile oxides leads to trialkylamino-(3-aryl-1,2,4-oxadiazol-5-yl)imides, while the corresponding reactions with sulfylcyanimines and phosphincyanimides do not take place. Using x-ray structural analysis the principal structural features of the 1,2,4-oxadiazole products have been elucidated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2084–2089, September, 1990.     

Syntheses with nitrile oxides. 2. Reaction of aromatic nitrile oxides with bis(trimethylsilylcarbodiimide)

The reaction of aromatic nitrile oxides with bis(trimethylsilylcarbodiimide) gives 5-amino-3-aryl-1,2,4-oxadiazoles.For previous communication, see [1].N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117334 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2430–2432, October, 1992.     

Reactions of sulfoxonium allylides with nitrile oxides and ring transformations of their reaction products

Reactions of allylides ($\text{1}$) with nitrile oxides ($\text{2}$) afforded furanylglyoxylate oxime ($\text{3}$) and 6H-l,2-oxazine ($\text{4}$). Ring transformations of $\text{3}$ and $\text{4}$ gave $\text{4}$ and pyrrolinone ($\text{6}$), respectively.     

Reaction of some aromatic nitrile oxides with dimedone

1,3-Dipolar cycloaddition of benzonitrile and m-nitrobenzonitrile oxides to the enol form of dimedone gives the corresponding 4-oxotetrahydrobenzisoxazoles. A second reaction path — nucleophilic addition of the enol to the N-oxide to give a hydroxamic acid derivative — is observed in the case of m-nitrobenzonitrile oxide. The tetrahydrobenzisoxazoles are converted to enamine derivatives of benzoyldimedone under catalytic hydrogenation conditions.     

Diastereoselective cycloadditions of a soluble polymer-supported substituted allyl alcohol derived from Baylis-Hillman reaction with nitrile oxides

A diastereoselective cycloaddition of a soluble polymer-supported Baylis-Hillman adduct with nitrile oxides is described. The reaction has shown to proceed with moderate diastereoselectivity, favoring the syn isomer of the resulting 3,5-substituted isoxazolines. The stereochemistry of the products has been assigned using ¹H NMR studies. The structure of one of the diastereomers has been determined by single-crystal X-ray crystallographic analysis.     

Reactions of nitrile oxides with nitrogen oxides. 1. Reactions with nitrogen tetroxide

We have studied the reaction of nitrile oxides with nitrogen tetroxide. It was shown that the reaction is selective: acetonitrile oxide yields ethylnitrolic acid, -oximinophenylacetonitrile oxide gives a mixture of isomers of phenylnitrofuroxan, and aromatic nitrile oxides give aryltrinitromethanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1620–1622, July, 1990.     

1,3-Dipolar cycloaddition reactions of nitrile oxides and nitrile imines with 2-methoxyvinyl phenyl ketone

Nitrile oxides react regioselectively with 2-methoxyvinyl phenyl ketone 1 to give 4-benzoylisoxazoles 4 via elimination of methanol from the primary cycloadducts 3 . After heating with an excess of nitrile oxide bis-cycloadducts 5 were also formed. Reactions of nitrile imines with 1 are less regioselective yielding both 4-benzoylpyrazoles 9 and 5-benzoytpyrazoles 10 , whereas no bis-cycloadducts were isolated.     

Study on the 1,3-dipolar cycloaddition reaction of 4-ethoxy-1,1,1-trifluoro-3-buten-2-one with nitrile oxides

1,3-Dipolar cycloaddition (1,3-DC) reaction of 4-ethoxy-1,1,1-trifluoro-3-buten-2-one 1 with nitrile oxides was studied. It was found that besides its CC participating in the formation of isoxazole rings, trifluoromethyl activated CO also underwent 1,3-DC reaction with nitrile oxides to afford 1,4,2-dioxazole rings. Single crystal diffraction analysis also evidenced the diheterocyclic configuration.     

Activation of nitriles by hydrogen bonding in cycloadditions with nitrile oxides

The dipolarophilic activity of aromatic nitriles in cycloaddition with benzonitrile oxides is remarkably enhanced by ortho-acylamino substituents. The activation depends upon the solvent and can be ascribed to a hydrogen bond which assists cycloaddition.     

Reaction of polyfluorinated cyclohexa-2,4-dienones with aryl nitrile oxides

Reaction of 1,3-dipolar cycloaddition of 6-chloropentafluorocyclohexa-2,4-dienone, 6-chloro-3-(pentafluorophenoxy)tetrafluorocyclohexa-2,4-dienone, and perfluoro-6-phenoxycyclohexa-2,4-dienone with aryl nitrile oxides proceeds highly stereoselectively at the c C=O group of the dienone providing in a high yield mixtures of diastereomeric fluorine-containing 3-aryl-1,4-dioxa-2-azaspiro[4,5]deca-2,6,8-trienes. The reaction of the latter with sodium pentafluorophenolate proceeds along the type of allyl substitution affording polyfluorinated 3-aryl-8-phenoxy-1,4-dioxa-2-azaspiro[4,5]deca-2,6,9-trienes.     

Cycloaddition of nitrile oxides to substituted vinylphosphonates

Cycloaddition of nitrile oxides to substituted vinylphosphonates was performed. A series of 4,5‐dihydroisoxazoles containing phosphonyl group were synthesized under very mild condition in excellent regiospecificity. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:309–311, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10149     

Amine-promoted cyclocondensation of highly substituted aromatic nitrile oxides with diketones

Base-promoted cyclocondensation of hindered nitrile oxides and cyclic diketones affords highly functionalized, sterically-encumbered isoxazole products in good yield. The mild reaction conditions (NEt₃, EtOH) are tolerant to a wide variety of functionality and permit the preparation of precursors to complex polycycles typically inaccessible via direct, intermolecular carboncarbon bond forming reactions. The ability to effect the cyclocondensation reaction with a catalytic amount of amine points to the intermediacy of an ammonium enolate as a key reactive species. A convenient, single step preparation of crystalline, stable nitrile oxides from the corresponding oximes enhances the advantages of this methodology for the preparation of functionalized polycycles.     

Stereoconvergent and stepwise 1,3-dipolar cycloadditions of nitrile oxides and nitrile imines

The first example of stereoconvergent 1,3-dipolar cycloaddition of nitrile oxides and nitrile imines with E/Z isomeric mixture of electron-deficient olefins is reported, delivering isoxazolines and pyrazolines bearing two vicinal stereogenic tertiary and trifluoromethylated quaternary carbon centers with perfect regioand diastereoselectivities. The possibility of concerted cycloaddition/epimerization sequence under basic condition to form the thermodynamically stable diastereomers is excluded th...