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Nitrone

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</style><div role="note" class="hatnote navigation-not-searchable">Not to be confused with <a href="Nitrene" title="Nitrene">nitrene</a>.</div>

In <a href="Organic_chemistry" title="Organic chemistry">organic chemistry</a>, a nitrone is a <a href="Functional_group" title="Functional group">functional group</a> consisting of an <a href="Amine_oxide" title="Amine oxide">N-oxide</a> of an <a href="Imine" title="Imine">imine</a>. The general structure is <style data-mw-deduplicate="TemplateStyles:r1123817410">

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</style>R1R2C=N+(−O−)(−R3), where R3 is not a <a href="Hydrogen" title="Hydrogen">hydrogen</a>. Their primary application is <a href="Chemical_Intermediate" class="mw-redirect" title="Chemical Intermediate">intermediates</a> in <a href="Chemical_synthesis" title="Chemical synthesis">chemical synthesis</a>. A nitrone is a <a href="1%2C3-dipole" title="1,3-dipole">1,3-dipole</a> used in <a href="1%2C3-dipolar_cycloaddition" class="mw-redirect" title="1,3-dipolar cycloaddition">cycloadditions</a>, and a <a href="Carbonyl_group" title="Carbonyl group">carbonyl</a> mimic.

<div class="mw-heading mw-heading2"><h2 id="Structure">Structure</h2></div>

Nitrones, as a tetrasubstituted <a href="Double_bond" title="Double bond">double bond</a>, admit <a href="Cis%E2%80%93trans_isomerism" title="Cis–trans isomerism">cis–trans isomerism</a>.<a href="#cite_note-:0-1">[1]</a>: 474

<div class="mw-heading mw-heading2"><h2 id="Generation_of_nitrones">Generation of nitrones</h2></div>

Typical nitrone sources are <a href="Hydroxylamine" title="Hydroxylamine">hydroxylamine</a> oxidation or <a href="Alkylimino-de-oxo-bisubstitution" class="mw-redirect" title="Alkylimino-de-oxo-bisubstitution">condensation</a> with <a href="Carbonyl_compounds" class="mw-redirect" title="Carbonyl compounds">carbonyl compounds</a>. Secondary hydroxylamines oxidize to nitrones in air over a timescale of several weeks, a process <a href="Copper_compounds" title="Copper compounds">cupric salts</a> accelerate.<a href="#cite_note-:0-1">[1]</a>: 476 <a href="#cite_note-:1-2">[2]</a>: 332–333 The most general reagent used for the oxidation of hydroxylamines is aqueous <a href="Mercuric_oxide" class="mw-redirect" title="Mercuric oxide">mercuric oxide</a>:<a href="#cite_note-:0-1">[1]</a>: 476 <a href="#cite_note-3">[3]</a>

However, a hydroxylamine with two <a href="Locant" title="Locant">α</a> hydrogens may unsaturate on either side. Carbonyl condensation avoids this ambiguity...<a href="#cite_note-4">[4]</a>

...but is inhibited if both ketone substituents are bulky.<a href="#cite_note-:0-1">[1]</a>: 477

In principle, N-<a href="Alkylation" title="Alkylation">alkylation</a> could produce nitrones from <a href="Oxime" title="Oxime">oximes</a>, but in practice <a href="Electrophile" title="Electrophile">electrophiles</a> typically perform a mixture of N- and O-attack.<a href="#cite_note-:0-1">[1]</a>: 479 <a href="#cite_note-:1-2">[2]</a>: 334

<div class="mw-heading mw-heading2"><h2 id="Reactions">Reactions</h2></div>

Some nitrones oligomerize:<a href="#cite_note-:0-1">[1]</a>: 483 <a href="#cite_note-:1-2">[2]</a>: 334,337-338 <a href="#cite_note-5">[5]</a> Syntheses with nitrone precursors obviate the issue with increased temperature, to exaggerate entropic factors; or with a nitrone excess.

<div class="mw-heading mw-heading3"><h3 id="Carbonyl_mimic">Carbonyl mimic</h3></div>

Like many other <a href="Unsaturated_compound" class="mw-redirect" title="Unsaturated compound">unsaturated</a> functional groups, nitrones activate the <a href="Locant" title="Locant">α and β carbons</a> towards reaction. The α carbon is an electrophile and the β carbon a nucleophile; that is, nitrones <a href="Polar_bond" class="mw-redirect" title="Polar bond">polarize</a> like carbonyls and nitriles but unlike <a href="Nitro_compound" title="Nitro compound">nitro compounds</a> and vinyl sulfur derivatives.<a href="#cite_note-:0-1">[1]</a>: 483 <a href="#cite_note-:1-2">[2]</a>: 338–340

Nitrones hydrolyze extremely easily to the corresponding carbonyl and N-hydroxylamine.<a href="#cite_note-:0-1">[1]</a>: 491 <a href="#cite_note-:1-2">[2]</a>: 344

<div class="mw-heading mw-heading3"><h3 id="1,3-dipolar_cycloadditions">1,3-dipolar cycloadditions</h3></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Nitrone-olefin_3%2B2_cycloaddition" class="mw-redirect" title="Nitrone-olefin 3+2 cycloaddition">Nitrone-olefin 3+2 cycloaddition</a></div>

As <a href="1%2C3-dipole" title="1,3-dipole">1,3‑dipoles</a>, nitrones perform <a href="1%2C3-dipolar_cycloaddition" class="mw-redirect" title="1,3-dipolar cycloaddition">[3+2] cycloadditions</a>.<a href="#cite_note-Yang_Synlett_2012-6">[6]</a> For example, a dipolarophilic <a href="Alkene" title="Alkene">alkene</a> combines to form <a href="Isoxazolidine" title="Isoxazolidine">isoxazolidine</a>:

Other <a href="Ring_closing_reaction" class="mw-redirect" title="Ring closing reaction">ring-closing reactions</a> are known,<a href="#cite_note-7">[7]</a> including formal [3+3] and [5+2] <a href="Cycloaddition" title="Cycloaddition">cycloadditions</a>.<a href="#cite_note-Yang_Synlett_2012-6">[6]</a>

<div class="mw-heading mw-heading3"><h3 id="Isomerization">Isomerization</h3></div>

Deoxygenating reagents, <a href="Photochemistry" title="Photochemistry">light</a>, or heat all catalyze rearrangement to the <a href="Amide" title="Amide">amide</a>. Acids catalyze rearrangement to the <a href="Oxime" title="Oxime">oxime ether</a>.<a href="#cite_note-:0-1">[1]</a>: 489–490 <a href="#cite_note-:1-2">[2]</a>: 345–347

<div class="mw-heading mw-heading3"><h3 id="Reduction">Reduction</h3></div>

<a href="Hydrides" class="mw-redirect" title="Hydrides">Hydrides</a> add to give <a href="Hydroxylamines" class="mw-redirect" title="Hydroxylamines">hydroxylamines</a>. <a href="Redox" title="Redox">Reducing</a> <a href="Lewis_acids_and_bases" title="Lewis acids and bases">Lewis acids</a> (e.g. <a href="Metals" class="mw-redirect" title="Metals">metals</a>, <a href="Sulfur_dioxide" title="Sulfur dioxide">SO2</a>) <a href="Deoxygenation" title="Deoxygenation">deoxygenate</a> to the <a href="Imine" title="Imine">imine</a> instead.<a href="#cite_note-:0-1">[1]</a>: 490 <a href="#cite_note-:1-2">[2]</a>: 343

<ul><li><a href="N-Oxoammonium_salt" title="N-Oxoammonium salt">N-Oxoammonium salt</a></li>

<li><a href="Nitronate" title="Nitronate">Nitronate</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFHamerMacaluso1964" class="citation journal cs1">Hamer, Jan; Macaluso, Anthony (1964-08-01). <a rel="nofollow" class="external text" href="https://pubs.acs.org/doi/abs/10.1021/cr60230a006">"Nitrones"</a>. Chemical Reviews. 64 (4): 473–495. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Fcr60230a006">10.1021/cr60230a006</a>. <a href="ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/0009-2665">0009-2665</a>.</cite>

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<li id="cite_note-:1-2">^ <a href="#cite_ref-:1_2-0">a</a> <a href="#cite_ref-:1_2-1">b</a> <a href="#cite_ref-:1_2-2">c</a> <a href="#cite_ref-:1_2-3">d</a> <a href="#cite_ref-:1_2-4">e</a> <a href="#cite_ref-:1_2-5">f</a> <a href="#cite_ref-:1_2-6">g</a> <cite id="CITEREFDelpierreLamchen1965" class="citation journal cs1">Delpierre, G. R.; Lamchen, M. (1965). <a rel="nofollow" class="external text" href="http://xlink.rsc.org/?DOI=qr9651900329">"Nitrones"</a>. Quarterly Reviews, Chemical Society. 19 (4): 329. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1039%2Fqr9651900329">10.1039/qr9651900329</a>. <a href="ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/0009-2681">0009-2681</a>.</cite>

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<li id="cite_note-3"><a href="#cite_ref-3">^</a> <cite id="CITEREFThiesingMayer1957" class="citation journal cs1">Thiesing, Jan; Mayer, Hans (1957). "Cyclische Nitrone, II. Über die Polymeren des 2.3.4.5-Tetrahydro-pyridin-N-oxyds und verwandte Verbindungen". <a href="Justus_Liebigs_Ann._Chem." class="mw-redirect" title="Justus Liebigs Ann. Chem.">Justus Liebigs Ann. Chem.</a> 609: 46-57. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1002%2Fjlac.19576090105">10.1002/jlac.19576090105</a>.</cite>

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<li id="cite_note-4"><a href="#cite_ref-4">^</a> <cite id="CITEREFExner1951" class="citation journal cs1">Exner, O. (1951). "A New Synthesis of N-methylketoximes". <a href="ChemPlusChem" title="ChemPlusChem">ChemPlusChem</a>. 16: 258-267. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1135%2Fcccc19510258">10.1135/cccc19510258</a>.</cite>

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<li id="cite_note-5"><a href="#cite_ref-5">^</a> <cite id="CITEREFThiesingMayer1956" class="citation journal cs1">Thiesing, Jan; Mayer, Hans (1956). "Cyclische Nitrone I: Dimeres 2.3.4.5-Tetrahydro-pyridin-N-oxyd". <a href="Chem._Ber." class="mw-redirect" title="Chem. Ber.">Chem. Ber.</a> 89 (9): 2159-2167. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1002%2Fcber.19560890919">10.1002/cber.19560890919</a>.</cite>

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<li id="cite_note-Yang_Synlett_2012-6">^ <a href="#cite_ref-Yang_Synlett_2012_6-0">a</a> <a href="#cite_ref-Yang_Synlett_2012_6-1">b</a> <cite id="CITEREFYang2012" class="citation journal cs1">Yang, Jiong (2012). "Recent Developments in Nitrone Chemistry". <a href="Synlett" title="Synlett">Synlett</a>. 23: 2293-97. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1055%2Fs-0032-1317096">10.1055/s-0032-1317096</a>.</cite>

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<li id="cite_note-7"><a href="#cite_ref-7">^</a> <cite id="CITEREFMurahashiImada2019" class="citation journal cs1">Murahashi, Shun-Ichi; Imada, Yasushi (15 March 2019). "Synthesis and Transformations of Nitrones for Organic Synthesis". Chemical Reviews. 119 (7): 4684–4716. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Facs.chemrev.8b00476">10.1021/acs.chemrev.8b00476</a>. <a href="PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/30875202">30875202</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:80623450">80623450</a>.</cite>

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