Nitroaldol Reaction - Modifications

Modifications

There have been a series of modifications made to the Henry Reaction. Of these some of the most important include employing high-pressure and sometimes solvent free conditions to improve chemo- and regioselectivity and chiral metal catalysts to induce enantio-or diastereoselectivity. The aza-Henry reaction is also used to produce nitroamines and can be a reliable synthetic route for the synthesis of vicinal diamines.

Perhaps one of the most synthetically useful modifications to the Henry Reaction is the use of an organocatalyst. The catalytic cycle is shown below.

List described that while this is a broad explanation, his brief review illustrates that this is a plausible mechanistic explanation for almost all reactions that involve an organocatalyst. An example of this type of reaction is illustrated in the Examples section of this article.

In addition to the previously mentioned modifications to the Henry reaction there are a variety of others. This includes the conversion of unreactive alkyl nitro compounds to their corresponding dianions which will react faster with carbonyl substrates, reactions can be accelerated using PAP as base, utilization of the reactivity of aldehydes with α,α-doubly deprotonated nitroalkanes to give nitronate alkoxides that yield mainly syn-nitro alcohols once protonated, and finally generation of nitronate anions in which one oxygenatom on the nitro group is silyl-protected to yield anti-β-nitro alcohols in the presence of a fluoride anion source when reacted with an aldehyde.