Five-Membered Ring Systems with O and N Atoms

Collision Induced Dissociation of Deprotonated Isoxazole and 3-Methyl Isoxazole via Direct Chemical Dynamics Simulations

“…Isoxazoles (C 3 H 3 NO) are aromatic five-membered ring molecules with a weak N−O bond and an important structural unit of numerous naturally occurring biomolecules. 1,2 The parent molecule and its derivatives have an important place in the pharmaceutical and agrochemical industries and play a vital role in organic synthesis. 3−7 Hu et al have reviewed the synthesis and functionalization of isoxazoles under different conditions.…”

“…Five- and six-membered heterocyclic ring molecules play pivotal roles as building blocks of life. Isoxazoles (C 3 H 3 NO) are aromatic five-membered ring molecules with a weak N–O bond and an important structural unit of numerous naturally occurring biomolecules. , The parent molecule and its derivatives have an important place in the pharmaceutical and agrochemical industries and play a vital role in organic synthesis. − Hu et al have reviewed the synthesis and functionalization of isoxazoles under different conditions . A wide variety of anti-inflammatory, antiviral, and HIV inhibitor drugs contain the isoxazole ring. , Due to the broad range of applications, these molecules have been subjected to numerous experimental and theoretical investigations.…”

Reaction of 1,3-Bis(het)arylmonothio-1,3-diketones with Sodium Azide: Regioselective Synthesis of 3,5-Bis(het)arylisoxazoles via Intramolecular N–O Bond Formation

“…The isoxazole motif is a privileged heterocyclic scaffold present in a plethora of natural products (ibotenic acid, muscimol, isoxazole-4-carboxylic acid) and synthetic compounds, , displaying a broad range of biological and pharmacological activities, thus emerging as a key structure in drug discovery, agrochemicals, as well as in material science. The isoxazole framework constitutes the core structure of many marketed drugs such as valdecoxib/parecoxib (COX2 inhibitor, antiinflammatory), sulfamethoxazole (antibacterial), leflunomide (antirheumatic), isocarboxazid (antidepressant), antibiotics oxacillin, cloxacillin, flucoxacillin, and micafungin (antifungal) (Figure ).…”

“…Although numerous methods have been reported for the synthesis of isoxazoles, ,, [3 + 2] dipolar cycloaddition of nitrile oxides with alkynes is probably the most direct route to access these heterocycles. , However, the nitrile oxides themselves are typically prepared, sometimes from unstable hydroximinoyl chloride, oximes, or by dehydration of nitroalkanes under frequently harsh conditions. , Besides, the uncatalyzed thermal cycloaddition of nitrile oxides with alkynes is neither chemo- nor regioselective, and as a consequence, leads to the formation of multiple products. Regioselectivity in these [3 + 2] cycloaddition reactions has been achieved using copper − or ruthenium catalysts .…”

Enolate-mediated 1,3-dipolar cycloaddition reaction of β-functionalized ketones with nitrile oxides: direct access to 3,4,5-trisubstituted isoxazoles

“…1, isoxazole compounds exhibit some biologically and pharmacologically important properties, such as anticancer, antianaphylactic and antitumor activity. 3,4 The most powerful protocol for the synthesis of isoxazole is the cycloaddition of nitrile oxides with alkynes under thermal conditions (Scheme 1 (1)). 5 Nevertheless, poor regioselectivity is obtained because of the high activation energy.…”