Oxide Cycloaddition Research Articles

Chiral Phosphoric Acid Catalyzed [3 + 2] Cycloaddition and Tandem Oxidative [3 + 2] Cycloaddition: Asymmetric Synthesis of Substituted 3-Aminodihydrobenzofurans.

Asymmetric [3 + 2] cycloaddition of quinones with ene- and thioene-carbamates was achieved by chiral phosphoric acid catalysis, providing the corresponding 3-amino-2,3-dihydrobenzofurans in excellent yields with moderate to good diastereoselectivities and excellent enantioselectivities. An asymmetric tandem oxidative cycloaddition protocol starting from hydroquinones was also accomplished with phenyliodine(III) diacetate and a chiral phosphoric acid in the same reaction vessel.

Oxidative Cycloaddition of Aldoximes with Maleimides using Catalytic Hydroxy(aryl)iodonium Species

AbstractA mild catalytic procedure for the efficient oxidative cyclization of aldoximes with maleimides mediated by hypervalent iodine(III) active species has been developed. This catalytic cyclization affords the corresponding pyrrolo‐isoxazole products in generally good yields. The catalytic cycle involves active hydroxy(aryl)iodonium species generated in situ from 2‐iodobenzoic acid as precatalyst and m‐chloroperoxybenzoic acid (m‐CPBA) as terminal oxidant in the presence of trifluoromethanesulfonic acid. The presence of active hydroxy(aryl)iodonium species in this reaction has been confirmed by ESI‐mass spectrometry and 1H NMR spectroscopy.magnified image

Two new entries to the ABF tricyclic ring system of 7,17-seco-type C19-diterpenoid alkaloids via free radical cyclization and [3+2] cycloaddition of nitrile oxide

Two new approaches for the construction the ABF ring systems of 7,17-seco-type C19-diterpenoid alkaloids have been successfully developed by using free radical cyclization and intramolecular nitrile oxide cycloaddition, respectively, as the key steps. Both methods would probably provide alternative strategies for the elaboration of AEF-rings in the total synthesis of 7,17-seco-type C19-diterpenoid alkaloids based on our previously prepared BCD ring systems.

ChemInform Abstract: Regioselective Synthesis of Triazoles via Base‐Promoted Oxidative Cycloaddition of Chalcones with Azides in Aqueous Solution.

A base-promoted oxidative cycloaddition of chalcones with azides in aqueous solution has been developed under transition-metal-free conditions, which provides a green method for the regioselective synthesis of trisubstituted triazoles in good yields.

ChemInform Abstract: Selectfluor Promoted NHC—Oxazoline Gold(I) Complex Catalyzed Cycloaddition/Oxidation Reaction of Enynones with Alkenes.

AbstractA variety of axial chiral NHC‐oxazoline gold(I) complexes are synthesized and combined with Selectfluor in situ to catalyze the oxidative cycloaddition reaction of enynone and alkenes with air as green oxidant.

Remote Stereoinductive Intramolecular Nitrile Oxide Cycloaddition: Asymmetric Total Synthesis and Structure Revision of (-)-11β-Hydroxycurvularin.

The first total synthesis and structure revision of (-)-11β-hydroxycurvularin (1b), a macrolide possessing a β-hydroxyketone moiety, were accomplished. The β-hydroxyketone moiety in this natural product was introduced by cleavage of the N-O bond in an isoxazoline ring that was formed diastereoselectively in a 1,5-remote stereocontrolled fashion by employing intramolecular nitrile oxide cycloaddition.

Water‐Assisted Nitrile Oxide Cycloadditions: Synthesis of Isoxazoles and Stereoselective Syntheses of Isoxazolines and 1,2,4‐Oxadiazoles

AbstractConventional methods generate nitrile oxides from oxime halides in organic solvents under basic conditions. However, the present work revealed that water‐assisted generation of nitrile oxides proceeds under mild acidic conditions (pH 4–5). Cycloadditions of nitrile oxides with alkynes and alkenes easily occurred in water without using catalysts, thus yielding isoxazoles and isoxazolines, respectively, with excellent stereoselectivity toward five‐ and six‐membered cyclic alkenes. A double stereoselective cycloaddition of two units of a nitrile oxide with cyclohexene was also achieved, thus yielding 1,2,4‐oxadiazole derivatives having a unique hybrid isoxazoline‐oxadiazole skeleton. Enantiomerically pure isoxazolines were prepared from monoterpenes with a ring strain. In one case, the isoxazoline with a butterfly‐like structure was simply prepared, and it might be used as a ligand in asymmetric catalysis.

Water-Assisted Nitrile Oxide Cycloadditions: Synthesis of Isoxazoles and Stereoselective Syntheses of Isoxazolines and 1,2,4-Oxadiazoles.

Conventional methods generate nitrile oxides from oxime halides in organic solvents under basic conditions. However, the present work revealed that water-assisted generation of nitrile oxides proceeds under mild acidic conditions (pH 4-5). Cycloadditions of nitrile oxides with alkynes and alkenes easily occurred in water without using catalysts, thus yielding isoxazoles and isoxazolines, respectively, with excellent stereoselectivity toward five- and six-membered cyclic alkenes. A double stereoselective cycloaddition of two units of a nitrile oxide with cyclohexene was also achieved, thus yielding 1,2,4-oxadiazole derivatives having a unique hybrid isoxazoline-oxadiazole skeleton. Enantiomerically pure isoxazolines were prepared from monoterpenes with a ring strain. In one case, the isoxazoline with a butterfly-like structure was simply prepared, and it might be used as a ligand in asymmetric catalysis.

ChemInform Abstract: A Novel Protocol for the Facile Construction of Tetrahydroquinoline Fused Tricyclic Frameworks via an Intramolecular 1,3‐Dipolar Nitrile Oxide Cycloaddition Reaction.

AbstractThe successful development of an efficient method for the construction of fused tricyclic tetrahydroisoxazoloquinoline scaffolds involving an intramolecular 1,3‐dipolar nitrile oxide cycloaddition reaction utilizing Baylis—Hillman derivatives in good yields is achieved for the first time.

Oxidative (3 + 2) Cycloaddition Reactions of Diaza-Oxyallyl Cationic Intermediates and Indoles for the Synthesis of Imidazoloindolines.

An oxidative diaza-(3 + 2) cycloaddition reaction of simple urea derivatives with substituted indoles has been developed. This transformation provides rapid access to highly functionalized imidazoloindolines that are represented in bioactive compounds. The reported method is compatible with a wide variety of functional groups and directly provides unique heterocyclic scaffolds from indoles and a simple urea derivative.

ChemInform Abstract: Rh(III)‐Catalyzed [5 + 1] Oxidative Cycloaddition of Arylguanidines with Alkynes: A Novel Access to C4‐Disubstituted 1,4‐Dihydroquinazolin‐2‐amines.

A novel and mild RhIII-catalyzed [5+1] oxidative cycloaddition between arylguanidines and alkynes efficiently affords C4-disubstituted 1,4-dihydroquinazolin-2-amines. Members of this family of heterocycles, which contain the relevant cyclic guanidine units, have shown interesting pharmacological properties. The mechanism probably involves the formation of an eight-membered rhodacycle in which the imine unit of guanidine is coordinated to the Rh center. This rhodacycle would evolve to give the C-4 disubstituted 1,4-dihydroquinazolin-2-amine skeleton.

Copper Acetate Catalyzed Regio­selective Synthesis of Substituted 1,2,3‐Triazoles: A Versatile Azide–Alk­ene Cycloaddition/Oxidation Approach

AbstractA copper acetate catalyzed oxidative cycloaddition reaction of benzyl and aryl azides with terminal and internal olefins that contain electron‐withdrawing groups (COOR, CONH2, CN, CHO, COR) has been developed. The reaction employs air as the oxidant and does not require any base or additives to afford 1,4‐disubstituted and 1,4,5‐trisubstituted 1,2,3‐triazoles in good to excellent yields with high regioselectivity.

Base-Promoted Oxidative Cycloaddition Reaction of [60]Fullerene with Ethyl Acetoacetate for C60 Bis-2',3'-dihydrofuran Derivatives: Effect of Bulky Addends.

The base-promoted oxidative cycloaddition reaction of [60]fullerene with ethyl acetoacetate was investigated. The reaction resulted in C60 bis-2',3'-dihydrofuran derivatives, but only with the trans-1, trans-2, trans-3, and e configurations rather than any cis or trans-4 structures, demonstrating a new regioselectivity resulting from steric influence on C60 bisaddition. In addition, distribution of the bisadducts was complicated by the unsymmetrical nature of the addends, where each individual configuration may consist of several regioisomers.

Synthesis of Isoxazoline Derivatives Based on Nitrile Oxide Cycloaddition of Nitroso‐Nitro‐Enamine

AbstractA new and stable nitroso‐nitro‐enamine reagent, providing a nitrile oxide 1,3‐dipole, has been treated with dipolarophiles in the course of 1,3‐dipolar cycloaddition reactions to give a large number of novel isoxazolyl‐pyrroline derivatives. Surprisingly, instead of the expected 2‐isoxazolyl‐dihydropyrrole cycloadducts, dihydropyrrol‐3‐one oximes were isolated as the main products in most cases. The imino‐oxime moiety was successfully transformed into 3‐aminopyrrole derivatives. The mechanism and selectivity of the reactions were also studied by experimental and theoretical methods [WB97XD/6‐311++G(2d,2p)//B3LYP/6‐311++G(2d,2p)], including the solvent effect.

Synthesis of Bicyclic Isoxazoles and Isoxazolines via Intramolecular Nitrile Oxide Cycloaddition.

An efficient and straight forward procedure for the syntheses of bicyclic isoxazole/isoxazoline derivatives from the corresponding dimethyl-2-(2-nitro-1-aryl/alkyl)-2-(prop-2-yn-1yl)malonates or dimethyl 2-allyl-2-(2-nitro-1-aryl/alkyl ethyl)malonate is described. High yields and simple operations are important features of this methodology.

Aerobic Oxidative Cycloaddition of α-Chlorotosylhydrazones with Arylamines: General Chemoselective Construction of 1,4-Disubstituted and 1,5-Disubstituted 1,2,3-Triazoles under Metal-Free and Azide-Free Conditions.

A novel synthetic approach toward 1,4-disubstituted 1,2,3-triazoles and 1,5-disubstituted 1,2,3-triazoles by aerobic oxidative cycloaddition of α-chlorotosylhydrazone with primary aryl amine has been developed. Significantly, the reaction proceeds smoothly to afford 1,4-disubstituted 1,2,3-triazoles and 1,5-disubstituted 1,2,3-triazoles under catalyst-free, metal-free, azide-free, and peroxide-free conditions.

ChemInform Abstract: Metal‐Free Iodine(III)‐Promoted Synthesis of Isoquinolones.

A metal-free oxidative cycloaddition reaction of substituted benzamides and alkynes has been developed for the synthesis of isoquinolones by using bis(trifluoracetoxy)iodobenzene (PIFA) and trifluoroacetic acid (TFA). Under mild conditions, a wide variety of isoquinolones were conveniently prepared via oxidative annulation of simple N-methoxybenzamide and diarylacetylene or aryl/alkyl acetylene derivatives in yields up to 87%.

ChemInform Abstract: One‐Step Synthesis of Tetrahydroindoles by Ceric(IV) Ammonium Nitrate‐Promoted Oxidative Cycloaddition of Enaminones and Vinyl Ethers.

Abstract A new and general one-step procedure to synthesize a variety of biologically interesting tetrahydroindole derivatives was successfully devised by reacting various β-enaminones with vinyl ethers in the presence of ceric(IV) ammonium nitrate as promoter. This novel synthetic method provides a facile and promising strategy to various tetrahydroindole derivatives in moderate to good yields.

Oxidative Additions of Homoleptic Tin(II) Amidinate

Seven tin(IV) amidinates were prepared and isolated from the reactions of tin(II) bisamidinate [Cy–NC(nBu)N–Cy]2Sn with a series of various 1,2-diones ((4 + 1) oxidative cycloaddition mechanism) an...

Rh(III)-catalyzed [5+1] oxidative cycloaddition of arylguanidines with alkynes: a novel access to C4-disubstituted 1,4-dihydroquinazolin-2-amines.

A novel and mild Rh(III)-catalyzed [5+1] oxidative cycloaddition between arylguanidines and alkynes efficiently affords C4-disubstituted 1,4-dihydroquinazolin-2-amines. Members of this family of heterocycles, which contain the relevant cyclic guanidine units, have shown interesting pharmacological properties. The mechanism probably involves the formation of an eight-membered rhodacycle in which the imine unit of guanidine is coordinated to the Rh center. This rhodacycle would evolve to give the C-4 disubstituted 1,4-dihydroquinazolin-2-amine skeleton.