N-Benzyl Aspartate Nitrones: Unprecedented Single-Step Synthesis and [3 + 2] Cycloaddition Reactions with Alkenes

Palladium-Catalyzed Synthesis of Nitrones Via Redox Cross-Coupling of Nitro Compounds and Alcohols

A novel methodology for the synthesis of nitrones via palladium-catalyzed redox cross-coupling of nitro compounds and alcohols is established. The protocol is a mild, convenient, ligand-free, and scalable synthesis method that can be compatible with various nitro compounds and alcohols. Nitrone is a significant multifunctional platform synthon which can be synthesized directly and efficiently via this tactic from commercially available and cheap raw materials.

B(C6F5)3-Catalyzed Diastereoselective and Divergent Reactions of Vinyldiazo Esters with Nitrones: Synthesis of Highly Functionalized Diazo Compounds

Herein we report a mild, transition-metal-free, highly diastereoselective Lewis acid catalyzed methodology toward the synthesis of isoxazolidine-based diazo compounds from the reaction between vinyldiazo esters and nitrones. Interestingly, the isoxazolidine products were identified to have contrasting diastereoselectivity to previously reported metal-catalyzed reactions. Furthermore, the same catalyst can be used with enol diazo esters, prompting the formation of Mukaiyama-Mannich products. These diazo products can then be further functionalized to afford benzo[b]azepine and pyrrolidinone derivatives.

Diastereoselective synthesis of atropisomeric pyrazolyl pyrrolo[3,4-d]isoxazolidines via pyrazolyl nitrone cycloaddition to facially divergent maleimides: intensive NMR and DFT studies

A pyrazolyl nitrone (2) underwent 1,3-dipolar cycloadditions to afford some N-substituted maleimides (3a-o). An atropisomeric character was introduced into the formed cycloadducts by using maleimides that have a restricted rotation around the C-N bond. Also, facial selectivity of both endo and exo cycloaddition was observed where the major atropisomer was one that is formed by attacking the nitrone from the less hindered face of the dipolarophile. On the other hand, maleimides with free rotation around the C-N bond led to endo and exo cycloadducts without atropisomerism. The presence of atropisomerism in the formed cycloadducts was confirmed by extensive NMR studies and DFT calculations.

Carbonyl-Directed Addition of N-Alkylhydroxylamines to Unactivated Alkynes: Regio- and Stereoselective Synthesis of Ketonitrones

A variety of ketonitrones were synthesized in moderate to excellent yields with high chemo-, regio-, and stereoselectivity by using carbonyl-directed addition of N-alkylhydroxylamines to unactivated alkynes under mild conditions. The product diverisity could be controlled by the use of different bases, and EtN( n-Pr)₂ could promote the formation of ketonitrones while using EtONa as base led to indanone-derived nitrones. Control experiments indicated that the carbonyl group of the substrate acted as an H-bond acceptor except for an electron-withdrawing group, and conjugated enone skeleton accounted for the high selectivity.

Stereoselective annulation between an allene, an alkene, and two nitrosoarenes to access bis(isoxazoliodine) derivatives

This work reports metal-free annulations between one allene, two nitrosoarenes and one electron-deficient alkene to afford bis(isoxazolidine) derivatives stereoselectively. This process involves an initial formation of isoxazolidin-4-imine oxides, followed by their dipolar [3 + 2]-cycloaddition with electron-deficient alkenes. To highlight the utility, the annulations of 5-alleneyl-1-enes with nitrosoarenes were also feasible to afford the desired bis(isoxazolidine) products with excellent stereocontrol. The resulting bis(isoxazolidine) products produced from two systems were reduced with Zn/MeOH to induce reductive N-O cleavages, yielding branched polyaminols stereoselectively.

Gold-catalyzed N,O-functionalization of 1,4-diyn-3-ols with N-hydroxyanilines to form highly functionalized pyrrole derivatives

This work describes new N,O-functionalization of 1,4-diyn-3-ols with N-hydroxyanilines to yield highly functionalized pyrrole derivatives.

Regioselectivity and diastereoselectivity of three-component reaction of α-amino acid, dialkyl acetylenedicarboxylates and 2-arylidene-1,3-indanediones

The 1,3-dipolar cycloaddition of active azomethine ylide, which were generated in situ from addition reaction of α-amino acids with dialkyl acetylenedicarboxylates, with 2-arylidene-1,3-indanediones showed versatile regioselectivity and diastereoselectivity. The reaction of sarcosine and glycine afforded one kind of functionalized spiro[indene-2,3'-pyrrolidines]. The other primary α-amino acids such as alanine, phenylalanine and leucine gave another kind of regioisomeric spiro[indene-2,3'-pyrrolidines]. The cyclic α-amino acids resulted in the corresponding spiro[indene-2,2'-pyrrolizines] and [indene-2,6'-pyrrolo[1,2-c]thiazoles].

New developments of ketonitrones in organic synthesis

Various vinyl ketonitrones are prepared using new strategies and were applied to synthesize heterocycles in organic synthesis.

Convenient synthesis of functionalized pyrrolo[3,4-b]pyridines and pyrrolo[3,4-b]quinolines via three-component reactions

A simple protocol for convenient construction of pyrrolo[3,4-b]pyridine skeleton was successfully developed by base promoted three-component reaction of β-enamino imide, aromatic aldehydes and malononitrile as well as its ester and amide derivatives.

Efficient synthesis of functionalized spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] via one-pot three-component reaction

Diverse functionalized spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] were efficiently synthesized by the three-component reaction of 3-arylamino-1-methyl-H-pyrrole-2,5-dione, isatins and malononitrile (ethyl cyanoacetate) in ethanol in the presence of triethylamine. This reaction not only provided a convenient synthetic method for the construction of a versatile spirooxindole system, but also access to reactive β-enaminone and its derivatives for organic and medical chemistry.

Synthesis of functionalized spiro[indoline-3,4'-pyridines] and spiro[indoline-3,4'-pyridinones] via one-pot four-component reactions

In the presence of triethylamine as catalyst, the one-pot four-component reactions of arylamines, methyl propiolate, isatin and malononitrile afforded the functionalized spiro[indoline-3,4’-pyridine] derivatives in good yields. Similar reactions with ethyl cyanoacetate successfully afforded the functionalized spiro[indoline-3,4’-pyridines] and spiro[indoline-3,4’-pyridinones] as the main products according to the structures of the arylamines and other primary amines.

One-pot synthesis of dihydrobenzisoxazoles from hydroxylamines, acetylenedicarboxylates, and arynes via in situ generation of nitrones

Aryne [3 + 2] cycloaddition with nitrones generated in situ from the addition of hydroxylamines to acetylenedicarboxylates affords moderate to good yields of dihydrobenzisoxazoles. This reaction extends the current scope of aryne cycloaddition to include in situ generated nitrones and produces functionalized dihydrobenzisoxazoles with a quaternary center.

Synthesis of 3,4-dihydropyridin-2(1H)-ones and 3,4-dihydro-2H-pyrans via Four-component reactions of aromatic aldehydes, cyclic 1,3-carbonyls, arylamines, and dimethyl acetylenedicarboxylate

A protocol has been developed for the efficient synthesis of structurally diverse 3,4-dihydropyridin-2(1H)-ones and 3,4-dihydro-2H-pyrans via four-component reactions of arylamines, acetylenedicarboxylate, aromatic aldehydes and cyclic 1,3-diketones. The selective formation of the very different pyridinone or pyran derivatives depends on the structure of cyclic 1,3-diketone. The key steps are proposed to involve Michael addition of the enamino ester formed in situ from the reaction of arylamine with dimethyl acetylenedicarboxylate to arylidine cyclic 1,3-diketones.

Simple reaction conditions for the formation of ketonitrones from ketones and hydroxylamines

The condensation of ketones and hydroxylamines to form ketonitrones was reinvestigated by using thermal conditions previously found to minimize hydroxylamine decomposition (t-BuOH, 110 degrees C). This simple approach allows the formation of exocyclic, acyclic, and alpha,beta-unsaturated ketonitrones with benzylic, linear, and branched nitrogen substituents in modest to excellent isolated yields.