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1,3-Dipolar cycloadditions of a number of C-aryl, C-carbamoyl-, and C,C-bis(methoxycarbonyl)nitrones and substituted Nvinylpyrroles proceed with high efficiency and regioselectivity with the formation of only one isomeric substituted 5-(1H-pyrrol-1- yl)isoxazolidine cycloadduct. [ABSTRACT FROM AUTHOR]

Palladium(II)-coordinated NCR¹ (R¹ = Et ( 1 ), NMe2 (2), Ph (3)) species react smoothly with acyclic nitrones such as the ketonitrones Ph2C=N(O)R⁴ (R⁴ = p-MeC6H4 (4), p-ClC6H4 (5)) and the aldonitrone p- MeC6H4CH=N(O)Me (6) in the corresponding nitrile media. This reaction proceeds as a consecutive two-step intennolecular cycloaddition to give the mono- and bis-2,3-dihydro-1,2,4-oxadiazole complexes [PdCl2(R¹CN){Na= C(R¹)ON(R⁴)Cb(R²R³)}](a-b) (7a-13a; R², R³ = Ph; R⁴ = C6H4Me-p, R¹ = Et (7), NMe2 (8), Ph (9); R⁴ = C6H4Cl-p, R¹ = Et (10), NMe2 (11), Ph (12); R² = H, R³ = C6H4Me-p, R4 = Me, R¹ = NMe2 (13)) and [PdCl2{Na= C(R¹)ON(R⁴)Cb(R²R³)}2](a-b) (7b-13b), respectively. Inspection of the obtained data and their comparison with the previous results indicate that the PdII centers provide substantially greater activation of RCN ligands toward the 1,3-dipolar cycloaddition than the relevant PtII centers. The palladium(II)- mediated 1,3-dipolar cydoaddition of ketonitrones to nitriles is reversible. All complexes were characterized by elemental analyses (C, H, N), high-resolution ESI-MS, and IR and ¹H and 13C{¹H} NMR spectroscopy. The structure of trans- 7b was determined by single-crystal X-ray diffraction. Metal-free 5-NR'2-2,3- dihydro-1,2,4-oxadiazoles (7c--13c) were liberated from the corresponding (2,3-dihydro-1,2,4-oxadiazole)2PdII complexes by treatment with 1,2-(diphenylphosphino)ethane, and the heterocycles were characterized by high-resolution ESI⁺-MS and ¹H and 13C{¹H} spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract The addition of Lewis acids changes the path of the reaction of N -vinylpyrroles with 3,4-dihydroisoquinoline- N -oxides: formal (3 + 3)-cycloaddition proceeds instead of (3 + 2)-cycloaddition. In the case of benzoyl(3,4-dihydroisoquinolin-2-ium-2-yl)amides, reaction path does not change in the same conditions, but changing of the diastereoselectivity occurs and other diastereomer of (3 + 2)-cycloaddition became predominant. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

The reactions of various nitrones with indolyl- and pyrrolylacrylates proceeds regioselectively with high diastereoselectivity in the case of aldonitrones, and represents an effective method for obtaining new indolyl- and pyrrolyl-substituted isoxazolidine carboxylates stabilized by weak (C H⋯O) and moderate (N H⋯N) strength intramolecular hydrogen bonding. The resulting cycloadducts exhibit promising in vitro anti-influenza activities. [ABSTRACT FROM AUTHOR]

1,3-Dipolar cycloaddition of benzylidenecyclopropane with various aldonitrones proceeds regioselectively giving good yields of 4-spirocyclopropane isoxazolidines. In the case of aldonitrones, bearing carbamoyl- or aryl-groups on the carbon atom, only the cis -isomer is formed. The compounds synthesized were tested for their virus-inhibiting activity. [ABSTRACT FROM AUTHOR]

Abstract: The first example of 1,3-dipolar cycloaddition reactions of nitrones with arylallenes is described. C-Carbamoylnitrones react with the C1 C2 double bond of arylallenes affording the corresponding 4-methyleneisoxazolidines in good yields. N-Aryl-C,C-bis(methoxycarbonyl)nitrones usually gave rearranged products: mixtures of 4,5-dihydro-4-oxo-1H-benzo[b]azepine-2,2(3H)dicarboxylates and 4-oxo-1,5-diarylpyrrolidine-2,2-dicarboxylates. [Copyright &y& Elsevier]

Abstract: The reactions of unactivated bis(methylene)cyclopropanes with nitrones and nitrile oxides have been investigated. The 1,1-diaryl-2-isopropylidene-3-methylenecyclopropanes react with the C,N-diarylnitrones to give a mixture of 2,2-dimethyl-1,6-diaryl-3-(diarylmethylene)piperidin-4-ones and 5-methyl-1-aryl-1-(arylamino)-4-(diarylmethylene)hex-5-en-3-ones. 2,3-Dihydro-3-methylenepyridin-4(1H)-ones are obtained by reaction of 1,1-diaryl-2-isopropylidene-3-methylenecyclopropanes with nitrile oxides. [Copyright &y& Elsevier]

Abstract: The first example of 1,3-dipolar cycloaddition reactions of nitrones to vinylidenecyclopropanes is described. The nitrones react with the C1′–C2′ double bond of vinylidenecyclopropanes to give the corresponding 4-cyclopropylidene-isoxazolidines in moderate yields. [Copyright &y& Elsevier]

Cycloaddition reactions of N -allyl substituted polycyclic derivatives of isoindole-1,3-dione with nitrones proceeds regio- and stereoselectively on the double bond of the N -allyl substituent giving substituted isoxazolidines with good yields. Regioselectivity of the cycloaddition of this dipolarophiles with nitrile oxides depends on the structure of unsaturated hydrocarbon scaffold and the reaction selectively leads to adducts on endocyclic or the double bond of the N -allyl substituent. DFT calculations were used to investigate the reasons of the selectivity. Image 1 • Regio- and stereoselectivity of the cycloaddition of N-allyl substituted derivatives of isoindole-1,3-dione with nitrones. • Dependence of the cycloaddition regioselectivity of nitrile oxides from the structure. • DFT calculations of the cycloaddition of nitrones and nitrile oxides. [ABSTRACT FROM AUTHOR]