Nitroalkene

A nitroalkene, or nitro olefin, is a functional group combining the functionality of its constituent parts, an alkene and nitro group, while displaying its own chemical properties through alkene activation, making the functional group useful in specialty reactions such as the Michael reaction or Diels-Alder additions.

Synthesis

Nitroalkenes are synthesized by various means, notable examples include:

• Nitroaldol reactions such as the Henry reaction:

File:Furfural nitroaldol condensation.png

• Nitration of an alkene with nitryl iodide generated in-situ from silver nitrite and elemental iodine:

File:Nitrogenation of a phenylisopropene.png

• Direct nitration of alkenes with nitric oxide and an aluminum oxide catalyst in acidic conditions:

File:Direct nitration of styrene with alumina catalyst.svg

• Direct nitration of alkenes with Clayfen (Iron(III) nitrate supported on Montmorillonite clay):

File:Direct nitration of styrene using FeNO3 on a Clayfen support.png

• Dehydration of nitro-alcohols:

File:Dehydration of 2-nitroethanol to nitroethylene via phthalic anhydride.svg

Reactions

Nitroalkenes are useful intermediates for various chemical functionalities.

• A nitroalkene behaving as a Michael acceptor in the synthesis of Lycoricidine:

File:Michael acceptor intermediate in Lycoricidine Synthesis.svg

• Nitroalkene acting as an activated dienophile toward butadiene in a Diels-Alder cycloaddition:

File:Nitroalkene dienophile in cycloaddition with butadiene.svg

• The synthesis of pyrrole derivatives via the Barton–Zard reaction:

File:Barton-Zard reaction.svg

• Pericyclic reaction of a nitroalkene yielding an indole:

File:Pericyclic reaction of a nitroalkene yielding an indole.svg

• Partial hydrogenation to an alkene baring a hydroxylamine functional group:

File:Partial hydrogenation of a nitrostyrene to an alkene hydroxylamine.svg

• Reduction to primary amines:

File:Hydrogenation of a nitrostyrene to a primary amine.svg

• Asymmetric Stetter reaction:

File:Asymmetric Stetter Reaction with Nitroalkenes.png

Nitroalkynes

The related nitroalkynes are rather unstable, easily losing nitrogen dioxide radicals, rearranging to nitriles over −40 °C, or adding nucleophiles. Fewer than 20 had been synthesized before 2014. Nitration of metalloalkynes requires nearly-bare nitronium, i.e. nitronium tetrafluoroborate or nitric anhydride. In contrast, Tilden's reagent suffices to nitrosylate metalloalkynes; the products then oxidize to nitroalkenes in peroxyacids. Protected nitroalkene dehydroiodination occurs delicately in the gas phase.