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The nitroaldol reaction (often called Henry reaction after the Belgian chemist who first described it) or nitro-aldol reaction, is a classic carbon–carbon bond formation reaction, from the combination of a nitroalkane and an aldehyde or ketone in the presence of a base to form β-nitro alcohols. It is nearly analogous to the aldol reaction that had been discovered 23 years prior that couples two carbonyl compounds to form β-hydroxy carbonyl compounds known as "aldols" (aldehyde and alcohol).
The Henry reaction begins with the deprotonation of the nitroalkane on the α-carbon position forming a resonance stabilized anion. The pKa of most nitroalkanes is approximately 17. This is followed by alkylation of the nitroalkane with the carbonyl containing substrate to form a diastereomeric β-nitro alkoxide. The protonation of the alkoxide by the previously protonated base will yield the respective β-nitro alcohol as product.
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The nitroaldol reaction is commonly employed in the preparation of various nitro compounds and ketones.
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