nitroolefination

Nitroolefination is a class of reactions that synthesizes nitroolefins, vinyl compounds bearing a nitro group. The most common approach forms these nitroalkenes by a Henry-type condensation between carbonyl compounds (typically aldehydes, and less often ketones) and nitroalkanes. In this sequence, the nitroalkane is deprotonated to a nitronate, which adds to the carbonyl to give a β-nitroalkoxide. Protonation yields a β-nitro alcohol, which can be dehydrated under acidic or basic conditions to furnish the β-nitroolefin. Several one-pot or catalytic variants have been developed that either combine the steps or enable direct formation of the nitroolefin without isolating the intermediate alcohol.

Substrates and scope are diverse. Aldehydes are the primary substrates, including both aromatic and aliphatic examples; ketones are less reactive but can participate under forcing conditions. Nitromethane and other nitroalkanes (e.g., nitroethane) are common nucleophiles. Reaction conditions vary widely and may employ inorganic bases, organic bases, or organocatalysts in polar aprotic solvents such as DMSO, DMF, or acetonitrile. Enantioselective variants exist using chiral organocatalysts or metal-based systems to provide enantioenriched nitroolefins.

Applications and properties are notable. Nitroolefins are versatile intermediates in organic synthesis, serving as Michael acceptors in conjugate additions, in cycloadditions, and as precursors to diamines and other nitrogen-containing motifs after further transformation. The products can exist as E/Z isomers, and stereocontrol is an area of ongoing development. Limitations include substrate sensitivity, selectivity control, and the need for efficient dehydration to achieve high yields of the desired nitroolefin.