Manganese-Catalyzed 5-Endo-trig Oxygenative Cyclization of α,β-Unsaturated Oximes under Air and Ambient Conditions for the Synthesis of 4,5-Dihydroisoxazoles

The stereoselective 5-endo-trig oxygenative cyclization of α,β-unsaturated oximes was achieved using molecular oxygen (O2) and a manganese catalyst. Several 4-hydroxy-4,5-dihydroisoxazoles were obtained in high yields by directly incorporating O2 from the atmosphere (eliminating the necessity for a pure oxygen environment) and using an unprecedentedly low loading of Mn(acac)3 (as little as 0.020 mol %) without additional additives. Because of its desirable features, such as operational simplicity, inexpensive catalyst, mild reaction conditions (open flask conditions at room temperature), and broad substrate compatibility, this novel reaction provides an attractive synthetic approach to producing 4-hydroxy-4,5-dihydroisoxazoles.

Anionic Chiral Co(III) Complexes Mediated Asymmetric Halocyclization─Synthesis of 5-Halomethyl Pyrazolines and Isoxazolines

An asymmetric synthesis of 5-halomethyl pyrazolines and isoxazolines which bear a tertiary stereocenter by catalytic halocyclization of β,γ-unsaturated hydrazones and ketoximes is described. By using Brønsted acids of anionic chiral Co(III) complexes as catalysts, a variety of chiral 5-halomethyl pyrazolines and isoxazolines were obtained in good yields with high enantioselectivities (up to 99% yield, 97:3 er). Preliminary bioassay results indicated that several isoxazoline derivatives exhibited significant antifungal activities.

Oxime radicals: generation, properties and application in organic synthesis

N-Oxyl radicals (compounds with an N-O• fragment) represent one of the richest families of stable and persistent organic radicals with applications ranging from catalysis of selective oxidation processes and mechanistic studies to production of polymers, energy storage, magnetic materials design and spectroscopic studies of biological objects. Compared to other N-oxyl radicals, oxime radicals (or iminoxyl radicals) have been underestimated for a long time as useful intermediates for organic synthesis, despite the fact that their precursors, oximes, are extremely widespread and easily available organic compounds. Furthermore, oxime radicals are structurally exceptional. In these radicals, the N-O• fragment is connected to an organic moiety by a double bond, whereas all other classes of N-oxyl radicals contain an R2N-O• fragment with two single C-N bonds. Although oxime radicals have been known since 1964, their broad synthetic potential was not recognized until the last decade, when numerous selective reactions of oxidative cyclization, functionalization, and coupling mediated by iminoxyl radicals were discovered. This review is focused on the synthetic methods based on iminoxyl radicals developed in the last ten years and also contains some selected data on previous works regarding generation, structure, stability, and spectral properties of these N-oxyl radicals. The reactions of oxime radicals are classified into intermolecular (oxidation by oxime radicals, oxidative C-O coupling) and intramolecular. The majority of works are devoted to intramolecular reactions of oxime radicals. These reactions are classified into cyclizations involving C-H bond cleavage and cyclizations involving a double C=C bond cleavage.

Room temperature iron(ii)-catalyzed radical cyclization of unsaturated oximes with hypervalent iodine reagents

An iron(ii)-catalyzed radical cyclization of oximes with hypervalent iodine reagents was developed, which enabled the construction of the isoxazoline backbone.

General 5-Halomethyl Isoxazoline Synthesis Enabled by Copper-Catalyzed Oxyhalogenation of Alkenes

A general and efficient oxyhalogenation of unsaturated ketoximes has been achieved through copper catalysis with diethyl bromomalonate, N-chlorosuccinimide, and N-iodosuccinimide, yielding 5-chloromethyl, 5-bromomethyl, and 5-iodomethyl isoxazolines in good to excellent yields.

Synthesis of Isoxazolines by the Electrophilic Chalcogenation of β,γ-Unsaturated Oximes: Fishing Novel Anti-Inflammatory Agents

Herein, we describe a new strategy to prepare chalcogen-functionalized isoxazolines. The strategy involves the reaction of β,γ-unsaturated oximes with electrophilic selenium and tellurium species, affording 19 new selenium- and tellurium-containing isoxazolines in good yields after 1 h at room temperature. The method was efficiently extended to the synthesis of 5 new (bis)isoxazoline ditellurides. One of the prepared compounds, 3-phenyl-5-((phenylselanyl)methyl)-isoxazoline, demonstrated better anti-inflammatory and antiedematogenic effects than the reference drug Celecoxib.

Metal-Involving Synthesis and Reactions of Oximes

This review classifies and summarizes the past 10-15 years of advancements in the field of metal-involving (i.e., metal-mediated and metal-catalyzed) reactions of oximes. These reactions are diverse in nature and have been employed for syntheses of oxime-based metal complexes and cage-compounds, oxime functionalizations, and the preparation of new classes of organic species, in particular, a wide variety of heterocyclic systems spanning small 3-membered ring systems to macroheterocycles. This consideration gives a general outlook of reaction routes, mechanisms, and driving forces and underlines the potential of metal-involving conversions of oxime species for application in various fields of chemistry and draws attention to the emerging putative targets.

Copper-mediated oxysulfonylation of alkenyl oximes with sodium sulfinates: a facile synthesis of isoxazolines featuring a sulfone substituent

A novel and efficient Cu(OAc)₂-mediated oxysulfonylation of alkenyl oximes with sodium sulfonates was developed. The reactions are easy to conduct, occur under mild conditions, and form a broad range of sulfone-substituted isoxazolines in good yields.

Green Organocatalytic Synthesis of Isoxazolines via a One-Pot Oxidation of Allyloximes

A green, sustainable, organocatalytic, and efficient synthesis of isoxazolines from allyloximes was developed. A 2,2,2-trifluoroacetophenone-catalyzed oxidation of allyloximes, utilizing H₂O₂ as the green oxidant, was taken advantage of in order to introduce a cheap and environmentally friendly protocol for the synthesis of substituted isoxazolines. A variety of substitution patterns, both aromatic and aliphatic moieties, are well tolerated, leading to isoxazolines in moderate to excellent yields.

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.

Transition-metal-free oxychlorination of alkenyl oximes: in situ generated radicals with tert-butyl nitrite

Highly efficient transition-metal-free radical oxychlorination of alkenyl oximes with t-BuONO has been developed.

CuX2-mediated oxybromination/aminochlorination of unsaturated amides: synthesis of iminolactones and lactams

A CuX₂-mediated halocyclization of γ,δ-unsaturated amides for the synthesis of functionalized iminolactones and lactams respectively is described.