Electrooxidative [3 + 2] annulation of amidines with alkenes for the synthesis of spiroimidazolines

The electrooxidative [3 + 2] annulation of amidines with 2-arylideneindane-1,3-diones or 4-alkylidene pyrazolones is reported using NaI as a redox catalyst and electrolyte under constant current electrolysis in an undivided cell. The current strategy features excellent functional group tolerance, simple operation, and mild conditions, thus providing an environmentally benign and efficient access to spiroimidazolines in moderate to good yields.     

Urea mediated 5-substituted-1H-tetrazole via [3 + 2] cycloaddition of nitriles and sodium azide

A simple, new and convenient metal free procedure for the synthesis of 5-substituted 1H-tetrazoles using various nitriles and sodium azide in the presence of urea and acetic acid with good to high yields is developed. The reaction plausibly proceeds through in situ formation of urea azide active complex without toxic and/or expensive metal catalysts.     

3H-Pyrroles as a platform for the catalyst-free construction of dihydropyrrolo[2,1-b]oxazoles: [4 + 2]-cycloaddition vs [2 + 3]-annulation with 1-cyano-3-hydroxyalkynes

Non-aromatic pyrrole isomers, 3,3-dialkyl-2-aryl-3H-pyrroles, were reacted with 1-cyano-3-hydroxyalkynes under mild, catalyst-free conditions (20–60?°C) to regio- and stereoselectively afford (Z)-2-(dihydropyrrolo[2,1-b]oxazolylidene)acetonitriles in 62–82% yield, thus evidencing the preference for [2?+?3]-annulation over the [4?+?2]-Diels-Alder alternative. The reaction involves initial nucleophilic addition of the pyrrole moiety at the triple bond followed by tandem ring closure of an anionic intermediate.     

Choline chloride–ZnCl2: Recyclable and efficient deep eutectic solvent for the [2+3] cycloaddition reaction of organic nitriles with sodium azide

Herein we report first time choline chloride–zinc chloride based deep eutectic solvent is a green and efficient reaction medium for the [2+3] cycloaddition reaction of organic nitriles with sodium azide to afford the corresponding 5-substituted 1H-tetrazoles. The present method provides an environment-friendly route, short reaction times with excellent yields, safe process, and simple workup which make this method an attractive and useful contribution to the existing conventional processes for the synthesis of 5-substituted 1H-tetrazoles.     

Design and synthesis of spirobiisoxazoline dibenzoquinone derivatives via [3 + 2] double 1,3-dipolar cycloaddition reaction

“A series of novel spirobiisoxazoline dibenzoquinone derivatives were synthesized starting from 2,5-dimethoxybenzaldehyde in a six-step synthetic sequence”. The key step [3?+?2] double 1,3-dipolar cycloaddition of oxime chloride with allenoate was performed under mild reaction conditions using sodium carbonate at ambient temperature. This is the first innovative synthesis of Spirobiisoxazoline Dibenzoquinone system where quinone ring is alkylated to isoxazoline moiety.     

A silica-gel accelerated [4 + 2] cycloaddition-based biomimetic approach towards the first total synthesis of magterpenoid C

The first total synthesis of magterpenoid C has been realized via a silica gel accelerated biomimetic Diels-Alder reaction between β-myrcene and randaiol derived quinone. However, application of similar strategy towards magterpenoid B via a protective Diels-Alder reaction failed to deliver the natural product.     

Nickel-catalyzed [2 + 2] cycloaddition reaction using bisallenes

A nickel-catalyzed [2 + 2] cycloaddition of bisallenes has been described. Simple bisallenes are employed for the formation of “head to head” cycloadducts in the presence of Ni(0) with xantphos. The dienyl moiety in a product were applicable for various [4 + 2] cycloaddition reactions. Allene-allenamides under Ni-xantphos system gave the tricyclic compounds through sequential [2 + 2]–[4 + 2] cycloaddition reaction in highly stereoselective manner.     

Porphyrin-LEGO®: synthesis of a hexafullereno-diporphyrin using porphyrins programmed for [4+2]-cycloaddition

A hexafullereno-diporphyrinoid was obtained in a sequence of cycloaddition steps using porphyrins programmed for [4+2]-cycloaddition reactions and C(60)-fullerene.     

Enantioselectivity of the reaction of α-amino acids with sodium azide and triethyl orthoformate in the synthesis of tetrazoles

Russian Journal of Organic Chemistry -     

Enamine–azide [2+3]-cycloaddition as a method to introduce functional groups into fluorescent dyes

Fluorescent dyes are a significant research tool with various applications in modern science. However, many experiments require the preparation of covalent dye conjugates, which is impossible without the presence of a functional group on the dye molecule. Unfortunately, the introduction of such groups is often a complicated task. Herein, we report a novel approach for the introduction of functional groups into fluorescent dyes, based on the [2+3]-cycloaddition reaction of “terminal” enamines with azides. The synthesis of such “terminal” enamines is carried out by the condensation of formamide acetals with a methyl group that is influenced by a strong electron withdrawing group. Thus, the proposed functionalization technique requires only the presence of a methyl group in the relevant position of the initial non-functionalized fluorescent dye.     

γ-Fe_2O_3:A magnetic separable catalyst for synthesis of 5-substituted 1H-tetrazoles from nitriles and sodium azide

<正>An efficient route for the synthesis of 5-substituted 1H-tetrazole via[2+3]cycloaddition of nitriles and sodium azide is reported usingγ-Fe_2O_3 nanoparticles as a magnetic separable catalyst.Under optimized conditions,the moderate to good yields(71-95%) can be obtained.The catalyst can be easily separated by a magnet and reused for several circles.     

Three-component reaction for synthesis of functionalized spiro[indoline-3,4’-pyrano[3,2-h]quinolines]

The functionalized spiro[indoline-3,40-pyrano[3,2-h]quinolines] were efficiently prepared in high yields from three-component reaction of 8-hydroxyquinoline, isatins and malononitrile or ethyl cyanoacetate in ethanol at room temperature for about 12 h in the presence of piperidine.     

Highly stereoselective [3+2]-cycloaddition reaction of stabilised N,N′-cyclic azomethine imines with 3-nitro-2-phenyl-2H-chromenes: Synthesis of tetrahydrochromeno[4,3-c]pyrazolo[1,2-a]pyrazol-11-ones

The reactions of 3-nitro-2-phenyl-2H-chromenes with 2-arylmethylidene-5-oxopyrazolidin-2-ium-1-ides proceeded diastereoselectively to afford the corresponding tetrahydrochromeno[4,3-c]pyrazolo[1,2-a]pyrazol-11-ones in good yields as a result of the 1,3-dipolar cycloaddition reaction of stabilised N,N′-cyclic azomethine imines at the Δ³-bond of the chromene system.     

Synthesis of N-heterocycles via [4 + 3] cycloaddition of azomethine imine

Di, tri and tetra-nitrogen containing 7-membered heterocycles are the key building blocks for natural and medicinally active compounds. They are using as antidepressants, antiulcer, antibiotics, antiemetic and also used as herbicides and insecticides. These building blocks can be synthesized easily from [4 + 3] cycloadditon reaction of azomethine imine with the other suitable reacting partner. Research on this area is very much important as this area is not much explored till now. Hence, the synthetic literature survey towards the di-nitrogen containing heterocycles is paramount importance. Herein, we report numerous synthetic routes (metal catalyzed, metal free, asymmetric) of di-nitrogen containing 7-membered heterocycle through [4 + 3] cycloadditon reaction of the last 10 years (2011-2019).     

Stereoselective synthesis of 2-substituted 3-azabicyclo[3.2.0]heptan-2-ones by [2+2]-cycloaddition of N-allyl-β-N-keteniminium salts derived from (R)-vinylglycinol

A stereoselective synthesis of (1R,2R,5S)-2-benzyloxymethyl-3-azabicyclo[3.2.0]heptan-2-one was achieved, by intramolecular [2+2]-cycloaddition of (R)-vinylglycinol-derived N-allyl-β-N-keteniminium salts, with high facial diastereoselection. The regio- and stereochemical courses have been qualitatively investigated by Molecular Mechanics calculations.     

Design and synthesis of [1,2,4]-triazolo isoquinoline derivatives via 1, 3-dipolar [3 + 2] cycloaddition: Reaction of azomethine imine with ethyl cyanoformate as unknown protocol

A series of novel 1, 2, 4-triazolo isoquinoline derivatives (8a-8p) were synthesized starting from 2-phenylethan-1-ol derivative (1) in a 7 step synthetic sequence. The key step in the scheme involves 1, 3-dipolar [3?+?2] cycloaddition of azomethine imine and ethyl cyanoformate as unknown reaction protocol. We have demonstrated the hydrolysis of both ester and benzoyl group in a single step and the corresponding carboxylic acid derivatives were coupled with various amines to generate unknown 1, 2, 4-triazolo isoquinoline derivatives The structures of the compounds (8a-8p) were characterized by ¹H NMR, ¹³C NMR and HRMS analysis.     

A tactical approach for the synthesis of novel β-lactam-substituted,polycyclic-fused isoxazolidine derivatives via an intramolecular [3+2] cycloaddition reaction

The synthesis of functionalized β-lactam-substituted, tricyclic chromenoisoxazolidine and tetracyclic naphthopyranoisoxazolidine derivatives by intramolecular nitrone cycloaddition reaction is described. The O-allyl hydroxyaldehyde derivatives, obtained from Baylis–Hillman adducts (BHA) derived from β-lactam aldehyde underwent intramolecular cycloaddition reaction to give β-lactam-substituted, polycyclic isoxazolidine derivatives in good yield. All the products were confirmed by spectral analysis. The products with a β-lactam substituent may find good applications in biological chemistry.