Copper-Catalyzed Synthesis of Trisubstituted Isoxazoles via a Cascade Cyclization–Migration Process

Palladium-Catalyzed Cyclization/Alkenylation of Ynone Oximes with Vinylsilanes for the Assembly of Isoxazolyl Vinylsilanes

A palladium-catalyzed cascade cyclization/alkenylation for the assembly of synthetically valuable isoxazolyl vinylsilane derivative has been accomplished. Easily accessible ynone oximes, and available vinylsilane agents were used as the reaction starting materials This protocol features broad substrate scope, good functional group tolerance, and good step- and atom-economy. Remarkably, this approach provides a new approach for the construction of structurally diverse isoxazolyl-containing vinylsilanes with high molecular complexity, showing a promising application in synthetic and pharmaceutical chemistry.

Tunable Key [3 + 2] and [2 + 1] Cycloaddition of Enaminones and α-Diazo Compounds for the Synthesis of Isomeric Isoxazoles: Metal-Controlled Selectivity

The three-component reactions of enaminones, α-diazo esters/ketones, and t-butyl nitrite (TBN) for the switchable synthesis of isomeric isoxazoles have been realized. The catalysis with Cu(II) salt provides 3,4-disubsituted isoxazoles via [3 + 2] cycloaddition. On the other hand, the catalysis of Ag(I) with identical substrates leads to isomeric isoxazoles with reversed C3 and C4 substitution based on a key [2 + 1] cycloaddition.

Consecutive O-S/N-S Bond Cleavage in Gold-Catalyzed Rearrangement Reactions of Alkynyl N-Sulfinylimines

Gold-catalyzed reactions of alkynyl N-sulfinylimines were used to produce the corresponding 2H-azirines possessing sulfenyl and acyl groups at the 3-position of the azirine ring in good to excellent yields. These reactions involved internal transfer of the sulfinyl oxygen atom to form a thiooxime intermediate tethered to an α-oxo gold carbene moiety. Subsequent insertion of the carbene into the N-S bond resulted in ring construction.

Palladium-Catalyzed Acylation of Terminal Alkynes toward 3-Ynone-Linked Chlorophyll-a Derivatives and Their Optical Properties

The Pd-catalyzed acylation reactions of terminal 3-ethynyl moieties of chlorophyll-a (Chl-a) derivatives are described herein. Both acyl chlorides and acid anhydrides were valuable reagents for the coupling, resulting in the formation of π-conjugation extended Chl-a derivatives possessing a carbonyl-ethynyl group at the C3-position. The ultraviolet-visible absorption and fluorescence emission data were obtained in solution to evaluate the optical properties of the 3-ynone-linked Chl-a derivatives.

Synthesis of 3-Acyl-isoxazoles and Δ2-Isoxazolines from Methyl Ketones, Alkynes or Alkenes, and tert-Butyl Nitrite via a Csp3-H Radical Functionalization/Cycloaddition Cascade

A novel metal-free tandem Csp³-H bond functionalization of ketones and 1,3-dipolar cycloaddition has been developed. An efficient approach to a variety of oxazole and isoxazoline derivatives is demonstrated using the 1,3-dipolar cycloaddition of alkynes and alkenes to nitrile oxides generated by reactions of methyl ketones with tert-butyl nitrite. This new protocol provides access to a variety of isoxazolines with diverse functionalities. An isoxazole generated in this way was found to have significant antifungal activity.

Copper nitrate-mediated synthesis of 3-aryl isoxazolines and isoxazoles from olefinic azlactones

A copper nitrate-mediated [2 + 2 + 1] cycloaddition reaction was developed for the expedient synthesis of isoxazolines and isoxazoles from olefinic azlactones.

In situ generation of nitrile oxides from copper carbene and tert-butyl nitrite: synthesis of fully substituted isoxazoles

Herein, we present a novel [3 + 2] cycloaddition reaction of β-keto esters with nitrile oxides, which were generated in situ from copper carbene and tert-butyl nitrite. This three-component reaction provides new methodology for the direct synthesis of fully substituted isoxazole derivatives, featuring mild reaction conditions, readily accessible starting materials and simple operation. The experimental studies and DFT calculations suggest that the reaction starts with the generation of the key intermediate nitrile oxides, followed by a [3 + 2] cycloaddition reaction of β-keto esters to give the final isoxazole products.

Copper nitrate-mediated chemo- and regioselective annulation from two different alkynes: a direct route to isoxazoles

An efficient copper nitrate-mediated chemo- and regioselective annulation reaction of two different alkynes was developed to achieve polysubstituted isoxazoles.

TEMPO-catalyzed synthesis of 5-substituted isoxazoles from propargylic ketones and TMSN3

A novel and efficient TEMPO-catalyzed synthesis of 5-substituted isoxazoles from propargylic ketones and TMSN₃via the radical mechanism process is described. A plausible reaction mechanism for this process is proposed.

Synthesis of 3,4,5-trisubstituted isoxazoles via 1,3-dipolar cycloaddition/SO2 extrusion of benzoisothiazole-2,2-dioxide-3-ylidenes with nitrile oxides

An straightforward synthesis of 3,4,5-trisubstituted isoxazole derivatives via 1,3-dipolar cycloaddtion/SO₂ extrusion of benzoisothiazole-2,2-dioxide-3-ylidenes with nitrile oxides is reported using 4 Å molecular sieves as dehydrochlorinating agent.

A direct access to isoxazoles from ynones using trimethylsilyl azide as amino surrogate under metal/catalyst free conditions

A general access to isoxazoles with outstanding functional group compatibility from the readily available ynones using trimethylsilyl azide as an amino surrogate under exceptionally simple conditions is described.

Synthesis of 3,4,5-Trisubstituted Isoxazoles from Morita-Baylis-Hillman Acetates by an NaNO2 /I2 -Mediated Domino Reaction

An efficient NaNO2 /I2 -mediated one-pot transformation of Morita-Baylis-Hillman (MBH) acetates into alkyl 3-nitro-5-(aryl/alkyl)isoxazole-4-carboxylates is described. In a cascade event, initial Michael addition of NaNO2 to the MBH acetate furnishes the allylnitro intermediate which undergoes I2 -catalyzed oxidative α-CH nitration of the nitromethyl subunit followed by [3+2] cycloaddition to afford the title compounds. Structural elaborations of these highly substituted isoxazoles by SN Ar reactions and hydrogenolysis allows access to useful products.

New 3,4,5-trisubstituted isoxazole derivatives with potential biological properties

Eighteen new isoxazole derivatives were synthesized and fully characterized. Their biological activity against Bcl-2, Bax and p21^WAF-1 was tested.

An eco-friendly synthesis of novel 3,5-disubstituted-1,2-isoxazoles in PEG-400, employing the Et3N-promoted hydroamination of symmetric and unsymmetric 1,3-diyne-indole derivatives

PEG-400 proved to be a useful solvent for the mild and efficient synthesis of 3,5-disubstituted 1,2-isoxazoles derived from 1,3-diyne indoles. The scope and limitations of the reaction were also studied.

A metal-free synthesis of diaryl-1,2-diketones by C–C triple bond cleavage of alkynones

A novel and environmentally benign protocol for diaryl-1,2-diketones was developed.