Генри реакция

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The Henry Reaction also referred to as the nitro-aldol reaction is a classic carbon—carbon bond formation reaction in organic chemistry. The pKa of most nitroalkanes is approximately It is important to note that all steps of the Henry reaction are reversible. This is due to the lack of a committed step in the reaction to form product. It is for this reason that research has been geared towards modifications to drive the reaction to completion. One of the commonly accepted models for stereoselection without any modification to the Henry reaction is shown below where stereoselectivity is governed by the size of the R groups in the model ex. The R groups play a role in the transition state of the Henry reaction in that the larger the R groups are on each of the substrates, the more they will want to orient themselves away from each other commonly referred to as steric effects \\\\\\\\\\\\\\\[3\\\\\\\\\\\\\\\] \\\\\\\\\\\\\\\[9\\\\\\\\\\\\\\\]. Due to a number of factors, including the reversibility of the reaction, as well as the tendency for easy epimerization of the nitro-substituted carbon atom, the Henry Reaction will typically produce a mixture of enantiomers or diastereomers. It is for this reason that explanations for stereoselectivity remain scarce without some modification. The first example of an enatioselective nitroaldol reaction was reported in using Shibasaki catalysts. One of the many features of the Henry Reaction that makes it synthetically attractive is that it utilizes only a catalytic amount of base to drive the reaction. Additionally a variety of bases can be used including ionic bases such as alkali metal hydroxides, alkoxides, carbonates, and sources of fluoride anion e. It is important to note that the base and solvent used do not have a large influence on the overall outcome of the reaction. One of the main drawbacks of the Henry Reaction is the potential for side reactions throughout the course of the reaction. A general scheme of the Cannizzaro reaction is depicted below. 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 \\\\\\\\\\\\\\\[2\\\\\\\\\\\\\\\] and chiral metal catalysts to induce enantio-or diastereoselectivity. Perhaps one of the most synthetically useful modifications to the Henry Reaction is the use of an organocatalyst. 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. Industrial Application- In , Menzel and coworkers developed a synthetic route to obtaining L-Acosamine, the carbohydrate subunit of the anthracycline class of antibiotics \\\\\\\\\\\\\\\[6\\\\\\\\\\\\\\\] \\\\\\\\\\\\\\\[14\\\\\\\\\\\\\\\]. A diastereoselective variation of this reaction is depicted below. Organocatalysis- In , Hiemstra and coworkers explored the use of quinine derivatives as asymmetric catalysts for the reaction between aromatic aldehydes and nitromethane. Through the use of particular derivatives, they were able to induce direct enantioselection through the use of the proper catalyst. Biocatalysis - In , Purkarthofer et al. From Wikipedia, the free encyclopedia. The Nitro Group in Organic Synthesis. University of Wisconsin Chemistry Department. Retrieved 17 January Establishment of an absolute scale of acidities in dimethyl sulfoxide solution'. Journal of the American Chemical Society. Utilization in catalytic carbon-carbon bond-forming reactions and catalytic asymmetric nitroaldol reactions'. Retrieved from ' https: Coupling reactions Carbon-carbon bond forming reactions. Views Read Edit View history. This page was last edited on 3 November , at By using this site, you agree to the Terms of Use and Privacy Policy.

Генри реакция

Реакция Анри

Реакция Генри : Бензальдегид + Нитроалкан

АНРИ РЕАКЦИИ

Nitroaldol reaction