1,3-Dipolar cycloaddition reactions of 1,3,4-oxadiazin-6-ones with nitrile oxides

2,5-Diaryl-1,3,4-oxadiazin-6-ones 1 gave with nitrile oxides 2 1,2,4-oxadiazole derivatives 4 . When mesitonitrile oxide 2a was used, bis-adducts 3 were also formed. The cycloadditions showed a remarkable site selectivity towards one carbon nitrogen double bond. The structure of both adducts was fully characterized by X-ray analysis.     

1,3-Dipolar cycloaddition reactions of 4-arylidene-2-phenyl-1,4-dihydroimidazol-5-ones with nitrile oxides

Stable nitrile oxides add regioselectively to the carbon-carbon double bond of 4-arylidene-2-phenyl-1,4-dihydroimidazol-5-ones to afford spiro isoxazolines 3 . Compounds 3 are further hydrolysed to isoxazole derivatives.     

1,3-Dipolar cycloaddition reactions of 2-phenyl-4-arylidene-5(4H)-oxazolones with nitrile oxides

Stable nitrile oxides are added stereospecifically and regioselectively to the carbon carbon double bond of 2-phenyl-4-arylidene-5(4H)-oxazolones resulting spiro-derivatives 3, 5 . The spectral properties of the reaction products are discussed. The cycloadducts give several substituted isoxazolines via an opening of the oxazolone ring with nucleophilic reagents.     

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.     

1,3-Dipolar cycloaddition reactions of 1-methyl- and 1,3-dimethylindol-2-yl nitrile oxides

Reactions of the in situ prepared 1-methylindol-2-yl nitrile oxide ( 2a ) with dipolarophiles lead to isoxazolines 5 and isoxazoles 8 and to their chloro-derivatives 6 and 9 in good yields. Analogous reactions of the 1,3-dimethylindol-2-yl nitrile oxide ( 2b ) give the isoxazolines 10 and the isoxazoles 12 as main products as well as their oxidation products 11 and 13 in low yields. The mechanism of the reactions and the spectral elucidation of the cycloadducts are discussed.     

1,3-dipolar cycloaddition of nitrile oxides with 2-phenyl-4-ethoxymethylene-5(4H)-oxazolone

2-Phenyl-4-ethoxymethylene-5(4H)-oxazolone 1 reacts regioselectively with nitrile oxides to give cycloadducts 3 . Reactions of the cycloadducts 3 with nucleophiles lead to 4-aminoisoxazole derivatives.     

1,3-Dipolar cycloadditions of 2-thio-3-chloroacrylamides with nitrile oxides and nitrones

1,3-Dipolar cycloadditions of 2-thio-3-chloroacrylamides with nitrile oxides and nitrones is described. A series of novel isoxazolines are isolated from the nitrile oxide cycloadditions, whilst the isoxazolines generated from the nitrone cycloadditions undergo further ring opening to yield piperidines.     

1,3-Dipolar cycloaddition of nitrile oxides to N-vinylcarbazole: Regioselective formation of 5-(9-carbazolyl)-Δ2-isoxazolines

Aryl substituted nitrile oxides undergo 3 + 2 cycloaddition to N-vinyl carbazole to afford only one regioisomer, i.e., 3-aryl substituted 5-(9-carbazolyl)-Δ²-isoxazolines III in good yield.     

Pseudoesters and derivatives. XXV. 1,3-Dipolar cycloaddition of diazomethane to 5-methoxy-3-pyrrolin-2-ones

Cycloaddition of diazomethane to pyrrolinones 1a,b,d,e affords only one regioisomer as a mixture of the epimeric pyrrolopyrazolines 2 and 2 ′,4-Halo derivatives 1f,g react with diazomethane to give the two possible regioisomers 2 and 3. The regio- and stereochemistry of the adducts is evidenced by the ¹H-nmr data. The primary adducts originated from the halopyrrolinones suffer dehydrohalogenation to give aromatized products, which by further methylation give derivatives of type 7, 8, 10 and 11.     

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.     

1,3-Dipolar cycloaddition of diarylnitrones to 1-(4-nitrophenyl)-5H-pyrrolin-2-one

The reaction of diarylnitrones with 1-(4-nitrophenyl)-5H-pyrrolin-2-one to give 2-oxa-6-oxo-3-phenyl-4-(R-phenyl)-7-(4-nitrophenyl)-3,7-diazabicyclo(3,3,0)octanes has been examined. The structures of the products were established by NMR and IR spectroscopy, and x-ray diffraction studies. The stereoselectivity of the reaction is due to exo-approach of the reactants with cis-stereospecific addition of the trans-forms of the C,N-diarylnitrones to the pyrrolinone double bond.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1675–1678, December, 1990.     

First asymmetric cycloaddition of carbonyl ylides to vinyl sulfoxides and furan-2(5H)-ones

The Rh2(OAc)4-catalyzed reactions of o-(methoxycarbonyl)-alpha-diazoacetophenone with enantiomerically pure 5-ethoxy-3-p-tolylsulfinylfuran-2(5H)-ones 1a and 1b afford 4,10-epoxybenzo[4,5]cyclohepta[1,2-c]furan-3,9-diones 6a and 6b, in good or moderate yields and in a completely regioselective way. The pi-facial selectivity is complete for 1a, which only yields anti-6a adducts, and very high for 1b. The endo stereoisomers are favored with respect to the exo ones in both reactions. The sulfinyl group significantly increases the reactivity of the dipolarophile as it has been demonstrated by studying the behavior of 5-methoxyfuran-2(5H)-one (3).     

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.     

Regioselectivity in the 1,3-dipolar cycloaddition of nitrile oxides to alkylidenecyclopropanes.

The 1,3-dipolar cycloaddition of nitrile oxides to methylenecyclopropanes substituted on the exocyclic double bond gives prevalently or exclusively 4-spirocyclopropane isoxazolines when the substituent is arylic or alkylic group, 5-spirocyclopropane isoxazolines when the substituent is an electron-withdrawing group. Adducts 16 and 17 selectively rearrange photochemically to the enaminoenone 19.     

Regio- and stereoselective 1,3-dipolar cycloaddition of arylnitrile oxides to 5-acetoxy-2(5H)-furanone

Summary Arylnitrile oxides undergo regio- and stereo-specific 1,3-dipolar cycloaddition reactions with 5-acetoxy-2(5H)-furanone. In each case a single product3a–3g results from ananti approach to the 5-acetoxy substituent, the oxygen of the 1,3-dipole being attached to C-4 of furan. Under similar conditions 5-benzoyloxy-2(5H)-furanone yields3h–3i. The structures of the adducts were determined by¹H- and¹³C-NMR spectroscopy.

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Regio- und stereoselektive 1,3-dipolare Cycloaddition von Arylnitriloxiden mit 5-Acetoxy-2(5H)-furanon

Zusammenfassung Arylnitriloxide reagieren mit 5-Acetoxy-2(5H)-furanon in einer regio- und stereoselektiven 1,3-dipolaren Cycloaddition. In jedem der untersuchten Fälle ergaben sich die einheitlichen Produkte3a–3g als Folge eineranti-Annäherung an den 5-Acetoxysubstituenten, wobei der Sauerstoff des 1,3-Dipols an das C-4 des Furans addiert. Unter ähnlichen Bedingungen ergab 5-Benzoyloxy-2(5H)-furanon die Produkte3h–3i. Die Strukturen der Addukte wurden mittels¹H-und¹³C-NMR bestimmt.

     

Substrate-dependent divergent outcomes from catalytic reactions of silyl-protected enol diazoacetates with nitrile oxides: azabicyclo[3.1.0]hexanes or 5-arylaminofuran-2(3H)-ones

Dirhodium(II)-catalyzed reactions of silyl-protected enol diazoacetates with nitrile oxides exhibit high nitrile oxide substituent dependence in the production rearrangement products via dipolar cycloaddition and either the Neber rearrangement or the Lossen rearrangement.     

Directed regiospecificity of 1,3-dipolar cycloaddition of 2-diazopropane to 4- and 5-substituted pyridazin-3(2H)-ones

6-Methoxy-2-methylpyridazin-3(2H)-one ( 1 ) gave with 2-diazopropane ( 8 ) a mixture of 3H-pyrazolo[3,4-d]-pyridazin-4(5H)-one derivative 12 , as the main product, and -7(6H)-one derivative 10 , as the minor product. On the other hand, 4-substituted pyridazin-3(2H)-ones 2, 3 , and 4 gave 3H-pyrazolo[3,4-d]pyridazin-7(6H)-one 10 , exclusively, while 5-substituted pyridazin-3(2H)-ones 5, 6 , and 7 produced only the isomeric 3H-pyrazolo[3,4-H]pyridazin-4(5H)-one 12 . The 5-phenylsulfonyl derivative 13 gave with 8 by elimination of a molecule of nitrogen, followed by rearrangement, 1,2-diazepine derivative 15 and with an excess of 8 3H-pyrazolo[3,4-d][1,2]diazepine derivative 16. 1 ,2-Dimethylpyridazine-3,6-(1H,2H)-dione and its derivatives 18 and 19 produced 3H-pyrazolo[3,4-d]pyridazine-4,7(5H,6H)-dione derivative 23 , while from 17 and 1-diazoindane ( 24 ) the spiro compound 27 was obtained. The 1,2-dihydro and 3a,7a-dihydro intermediates 21 and 25 were isolated.     

Synthesis of 8,9-oxaza[5.3.3]Propell-9-en-2-ones via 1,3-dipolar cycloaddition of nitrile oxides to bicyclo[5.3.0]Dec-1(7)-en-2-one

The synthesis of the title heterocyclic propellanes is described. The cycloaddition is also examined on the basis of frontier molecular orbitals (FMO) of the reacting species.     

1,3-Dipolar cycle-addition of 2-diazoalkanes to pyridazin-3(2H)-one derivatives. The formation of 3H-pyrazolo[3,4-d]pyridazin-4(5H)-one and 3H-pyrazolo[3,4-d]pyridazin-7(6H)-one derivatives

1,3-Dipolar cycloadditions of diazoalkanes to pyridazin-3(2H)-ones 1–7 and pyridazin-3(2H)-thiones 8 and 9 are regioselective producing 3H -pyrazolo[3,4-d]pyridazin-4(5H)-ones 15–19, 27–29 and 34–38 as the major products. In some instances, the isomeric 3H-pyrazolo[3,4-d]pyridazin-7(6H)-ones, such as 20 and 23 were isolated as the minor products. From 3 and 6 the primary 3a,7a-dihydro cycloadducts 25 and 26 , and rearranged 1,2-dihydro intermediate 31 were isolated. From 10 and 1-diazoindane the isomeric exo- and endospiro products 39 and 40 were formed.