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A variety of functionalized 2‐pyrrolidinones bearing N‐trifluoromethylphenyl moieties were prepared in moderate to good yields with high diastereoselectivity through copper(II)‐catalyst and base co‐catalyzed formal [4+1] cycloaddition of cinnamaldehyde nitrones with 1‐ethynylnaphthalen‐2‐ols in the presence of m‐CPBA as the oxidant. The triple bond of 1‐ethynylnaphthalen‐2‐ol served as one‐carbon synthon for the pyrrolidinone ring formation. Mechanistic studies revealed that m‐CPBA played an important role to interrupt the intramolecular O‐cyclization to afford the 2‐pyrrolidinones. Moreover, the reaction could be easily performed at gram scales and the obtained products were selectively converted into diverse pyrroline scaffolds. [ABSTRACT FROM AUTHOR]

We described a copper(II)‐catalyzed [3+2] cycloaddition of N‐aryl‐α,β‐unsaturated nitrones with disubstituted allenoates bifurcated to prepare various [1,3]oxazino[3,2‐a]indolines and dihydropyrido[1,2‐a]indolines in moderate to excellent yields. Mechanistic studies revealed that [1,3]oxazino[3,2‐a]indoline was a kinetically favored product and dihydropyrido[1,2‐a]indoline was thermodynamically favored product. Moreover, the reaction was easily performed at gram scales and chiral dihydropyrido[1,2‐a]indoline could be obtained by using chiral auxiliary. The present method highlights broad substrate scope, good functional group tolerance, and diversity of indoline scaffolds with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

We describe a DBU‐controlled 6π‐azaelectrocyclization of dibenzylideneacetone‐derived N‐vinyl‐α,β‐unsaturated nitrones to prepare 6‐alkyl pyridine N‐oxides in 24–82% yields. Mechanistic studies revealed that DBU had a great impact on the formation of 6‐alkyl pyridine N‐oxides and served as a base and the carrier of hydrogen sources to in situ reduce C=C bonds. The 6‐alkyl pyridine N‐oxide was prepared at gram‐scales and converted to estrone‐derived pyridine and pyrido[2,3‐c]carbazole 4‐oxide in 46% and 52% yields in two steps, respectively. [ABSTRACT FROM AUTHOR]

Various spirooxindole‐benzo[d]oxazoles and dihydrobenzofurans were prepared in good to excellent yields by [3+2] cycloaddition and selective rearrangement of N‐vinyl oxindole nitrones and arynes under transition metal‐free conditions. Experimental results showed that the substituent on the nitrone N‐vinyl group controlled the [1,3]‐ or [3,3]‐rearrangement of their cycloadduct owing to its steric effect. The present method features broad substrate scope, good functional group tolerance, controllable [1,3]‐ or [3,3]‐rearrangement, and diverse oxindole scaffolds. [ABSTRACT FROM AUTHOR]

A variety of chiral nine‐membered N‐heterocycles were prepared in moderate to good yields with high diastereoselectivity through a silver(I)‐catalyzed [3+2] cycloaddition and [3,3]‐rearrangement of N‐vinyl‐α, β‐unsaturated nitrones and chiral 3‐propioloyloxazolidin‐2‐ones. Experimental studies showed that silver catalyst promoted the cycloaddition and rearrangement process, and the stereochemistry of the nine‐membered N‐heterocycles was controlled via [3,3]‐rearrangement by chiral oxazolidinone‐auxiliary through a boat‐like transition state. Moreover, the obtained nine‐membered N‐heterocycle diastereomers were converted to chiral pyrrolizines with high diastereoselectivity and pyrrolizine carboxylate was obtained in 54% yield with 90% ee by the removal of chiral auxiliary. [ABSTRACT FROM AUTHOR]

We report a relay catalysis for the highly stereoselective synthesis of densely substituted oxazonine-fused endoperoxides in good yields. This domino reaction is based on an Yb(OTf)3 and visible light promoted [3 + 2] cycloaddition/[3,3]-rearrangement, and in situ [4 + 2] cycloaddition with air in one pot under mild reaction conditions from N-vinyl-α,β-unsaturated nitrones and methylenecyclopropanes, leading to a practical assembly of densely substituted oxazonine-fused endoperoxides containing five stereocenters with a wide substrate scope and excellent diastereoselectivity. Mechanistic studies reveal that the O–O bond of the endoperoxide ring is derived from singlet oxygen (1O2) generated by air under a white LED. Moreover, such an asymmetric relay catalyst has also been realized to afford chiral endoperoxides in good enantioselectivity. Biological tests show that the designed oxazonine-fused endoperoxides significantly inhibited nitric oxide (NO) generation in LPS-stimulated RAW264.7 cells and exhibited their bioactivity as good anti-inflammatory agents. [ABSTRACT FROM AUTHOR]

We report a Yb(OTf)3‐catalyzed formal [7+2] cycloaddition for the preparation of nine‐membered N‐heterocycles bearing three stereocenters in good yields with high diastereoselectivity through a [3+2] cycloaddition/[3,3]‐rearrangement cascade strategy from N‐vinyl‐α,β‐unsaturated nitrones and methylenecyclopropanes. Preliminary studies show that the Yb(OTf)3 catalyst accelerates the reaction affording kinetically controlled cis‐diastereomers as the major products. The obtained nine‐membered N‐heterocycles are easily converted to useful derivatives for late‐stage modification. [ABSTRACT FROM AUTHOR]

A general protocol for the construction of novel densely functionalized γ-lactones was developed in good to excellent yields with high diastereoselectivity from easily available N-vinyl-α,β-unsaturated nitrones and ketenes. The reaction involves copper-catalyzed [5 + 2] cycloaddition, N–O bond cleavage, 6π electron cyclization, and aromatization to afford various γ-(pyridin-2-yl)lactones over four step transformations in a single flask. The present method features mild reaction conditions, high atom economy, high regio- and diastereoselectivity, diversity of γ-lactones, and a new application of the O-transfer reaction. [ABSTRACT FROM AUTHOR]

A variety of spirofluorenyl‐β‐lactams have been prepared in moderate yields over three steps from N‐aryl fluorenone nitrones and methylenecyclopropanes through a [3+2] cycloaddition, reduction and subsequent acid‐catalyzed ring contraction cascade strategy under mild reaction conditions. Experimental studies showed that the stereochemistry remained intact after the ring contraction step. Furthermore, the obtained spirofluorenyl‐β‐lactam was easily converted to two novel spiroazetidine and spiroquinolinone scaffolds in good yields. [ABSTRACT FROM AUTHOR]

A variety of (E)-N-aryloxindole nitrones were prepared in good to excellent yields by using a copper-catalyzed coupling reaction of isatin oximes and arylboronic acids under mild conditions. Various arylboronic acids that contain sensitive functional groups were tolerated in the transformation, and detailed studies show that the carbonyl group of the isatin oximes serves as a ligand to control the formation of the (E)-oxindole nitrones. This method to prepare (E)-N-aryloxindole nitrones was easily performed on a gram scale and efficiently used to synthesize estrone-derived oxindole nitrone in high yield. [ABSTRACT FROM AUTHOR]

A metal-free construction of highly diastereoselective nine-membered heterocycles is described via the cycloaddition and rearrangement of N-vinyl- α,β-unsaturated ketonitrones and isocyanates. Notably, the prepared nine-membered heterocycles afforded 2,3-dihydropyrrolizines under heating conditions. Mechanistic studies showed that the nine-membered rings might undergo decarboxylation, isomerization, aza-Michael addition, and aromatization to afford 2,3-dihydropyrrolizines in a one-pot reaction. [ABSTRACT FROM AUTHOR]

A single-flask procedure for the generation of α-keto- N-alkenylnitrones through a Chan-Lam coupling and subsequent spontaneous 6π electrocyclization of these intermediates for the synthesis of 2 H-1,4-oxazine N-oxides has been developed for a variety of α-ketooximes and alkenylboronic acids. This transformation provides a new approach to C-substituted unsaturated morpholine derivatives that are poised to undergo further functionalization for the preparation of a diverse array of novel heterocyclic structures. The scope of the new method for the synthesis of 2 H-1,4-oxazine N-oxides is discussed, in addition to initial studies describing the cycloaddition reactivity of these new heterocyclic intermediates. [ABSTRACT FROM AUTHOR]

An asymmetric method for the synthesis of dihydropyrido[1,2- a]indoles from mixtures of nitrones and allenoates has been developed. This transformation showcases the use of squaramide catalysis in a complicated cascade system that has been shown to be highly sensitive to reaction conditions and substituent effects. The new method provides access to enantiomerically enriched dihydropyridoindoles from modular, non-indole reagents. The optimization and scope of the new transformation is discussed in addition to initial mechanistic experiments that indicate the role of the catalyst. [ABSTRACT FROM AUTHOR]

A mild, metal-free,and modular route for the preparation of N-styrenylamidines from N-aryl-α,β-unsaturatednitrones and isocyanates has been developed that accesses an initialoxadiazolidinone intermediate that can undergo CO2eliminationand styrenyl migration. The use of a migration event to install N-styrenyl amidine substituents circumvents a limitationof traditional Pinner-type methods for amidine synthesis that requirethe use of amine nucleophiles. The modularity of the nitrone and isocyanatereagents provides access to a variety of differentially substituted N-styrenyl amidines. The scope and tolerance of the methodare presented, and preliminary mechanistic data for the transformationare discussed. [ABSTRACT FROM AUTHOR]

Please pass the oxygen: A new method for the preparation of trans‐α,β‐epoxyketimines has been achieved through a copper‐catalyzed rearrangement of (E)‐α,β‐unsaturated nitrones. The scope and tolerance of the method is evaluated and the synthetic utility of the products is demonstrated. The new transformation provides facile access to an unusual, densely functionalized intermediate that can be exploited for further synthetic application. [ABSTRACT FROM AUTHOR]

N-Vinyl nitrones derived from fluorenone have been prepared via a copper-mediated coupling between fluorenone oxime and vinyl boronic acids. These compounds undergo subsequent rearrangement and addition reactions that are distinct from the traditional [3 2] cycloaddition reactivity of nitrones. Thermal rearrangements of fluorenone N-vinyl nitrones give spiroisoxazolines, while treatment with alkynes provides fluorene-tethered isoxazoles. The scope and limitations of the preparation of fluorenone N-vinyl nitrones and their subsequent rearrangement and addition reactions are discussed. [ABSTRACT FROM AUTHOR]

α,β-Unsaturated nitrones (I) and (IV) undergo Cu(I)-catalyzed oxygen-atom transfer reaction to give α,β-epoxyketimines, generally with excellent trans-diastereoselectivity. [ABSTRACT FROM AUTHOR]

Derivatives (III) are prepared by means of Chan-Lam reaction. [ABSTRACT FROM AUTHOR]