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Amine synthesis by nitrile reduction - Organic chemistry

or aldehydes with NH 3 as a nitrogen source is a good candidate for the “green nitrile synthesis.” ..

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octanal (aldehyde C-8), 124-13-0 - The Good Scents …

This invention discloses a process for the synthesis of stable aryl nitrile oxides which comprises the sequential steps of (1) halomethylating a halomethyl group onto a substituted aromatic compound having at least one substituent group selected from the group consisting of alkyl groups, aryl groups, fused aryl groups, alkaryl groups, halogen atoms, alkoxy groups and nitro groups, wherein said halomethyl group is halomethylated onto a position that is ortho to at least one of the substituent groups on the substituted aromatic compound; (2) converting the ortho halomethylated-substituted aromatic compound into an ortho-substituted aromatic aldehyde by reacting the ortho halomethylated-substituted aromatic compound with a salt selected from the group consisting of sodium 2-nitropropane and potassium 2-nitropropane in a lower alcohol solvent; (3) converting the ortho-substituted aromatic aldehyde into an ortho-substituted aromatic oxime by reacting the ortho-substituted aromatic aldehyde with hydroxylamine; and (4) converting the ortho-substituted aromatic oxime into the ortho-substituted aryl nitrile oxide by reacting the ortho-substituted aromatic oxime with an aqueous sodium hypochlorite solution at a temperature which is within the range of about -5 DEG C to about 20 DEG C.

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Natural products that contain “oxidized” amides, in which the carbon bonded to the nitrogen atom has an oxidation state that is higher than the usual (+1) level, effect an impressive range of biological responses. These compounds are represented acyl hemiaminals such as the cytotoxins zampanolide (1) and tallysomycin, and acyl aminals such as the protein synthesis inhibitors psymberin (2) and pederin. These compounds have evoked substantial synthetic efforts, and several approaches to the synthesis of the oxidized amide groups and natural product total syntheses have been disclosed. SAR studies have demonstrated that oxidized amides are important for the biological activities of these natural products. While these groups have been proposed to serve as latent acyliminium ions only one report has appeared in the literature that compellingly establishes protein alkylation through Schiff base formation from an enamide, another important class of oxidized amide. In addition to their roles in conferring biological activity, acyl aminals have been used as latent electrophiles in stereoselective carbon–carbon bond forming reactions.

Strecker Synthesis - Organic Chemistry Portal

In principle oxidized amide groups can be prepared from acylimine intermediates (), with acyl aminals being accessed through alcohol addition and acyl hemiaminals being accessed through water addition. Additionally, enamides could be accessed through tautomerization. This strategy is limited, however, by the dearth of methods for preparing acylimines. Condensation reactions between aldehydes and amides are ineffective when the aldehyde is enolizable. While this problem can be addressed by adding sulfonates to form α-sulfonyl amides, regenerating and isolating the acylimine is difficult (though not impossible) because of the sensitivity of the intermediates.

“Oxidized” amides, as represented by acyl aminals and acyl hemiaminals, are integral subunits of several natural products that exhibit useful biological activity. In this manuscript a multicomponent approach to these groups from acylimine intermediates is demonstrated. The acylimines are accessed through a sequence of nitrile hydrozirconation and acylation, making this highly versatile amide synthesis useful for a range of range of applications in target- and diversity-oriented synthesis.

Mechanism of the Strecker Synthesis

In consideration of our interests in the synthesis of 1, 2, and related structures we sought to develop a universal approach to acylimine construction from easily handled precursors and to establish conditions for the preparation of each class of oxidized amide. Acylating metalloimines is an attractive approach to acylimine formation (). This route can be executed by preparing metalloimines from selective nitrile hydrometallation followed by acid chloride addition. Given the abundant reactions that have been developed for nitrile synthesis and the relatively inert nature of nitriles (compared to other electrophilic groups) to most reaction conditions, this strategy should be useful in the synthesis of complex natural products. Majoral and coworkers have reported that treating sterically hindered nitriles with Schwartz’ reagent (Cp2Zr(H)Cl) followed by adding sterically hindered acid chlorides yields isolable acylimines. In this manuscript we demonstrate that the sequence of nitrile hydrozirconation, acylation, and nucleophile addition results in a versatile multicomponent approach to oxidized amides.

To apply this process in a more complex setting that is relevant to the synthesis of psymberin, pederin, and analogs, we prepared () nitrile 29 from the known ketone 27 through a sequence that employs a Lewis acid-promoted reduction with Bu3SnH to establish relative stereocontrol to provide 28. Interestingly, the stereochemical outcome of this reaction does not follow from the chelation-control that is generally observed in this procedure. Tetrahydropyran formation through a sequence of ozonolytic alkene cleavage, acylation, and cyanide introduction yielded 29. Hydrozirconation, acylation with isobutyroyl chloride, and MeOH addition in the presence of Mg(ClO4)2 provided acyl aminal 30 in 54% yield, diastereomer 31 in 23% yield, and a small amount (~10%) of the amide that arises from reduction of the intermediate acylimine with the slight excess of Schwartz’ reagent that is used in these reactions. Stereochemical assignments were based on 1H NMR splitting pattern and chemical shift analogies to known compounds in the pederin/psymberin family. While chelation controlled addition could not be promoted to the same extent as was observed for 10, the high overall chemical yield and reasonable stereocontrol provide the desired acyl aminal with the desired stereochemical orientation efficiently and with the potential for extensive structural variation. Also notable in this transformation was the absence of epimerization at the carbon that bears the cyano group, indicating that these conditions do not erode the stereochemical purity of cyanohydrin ethers.

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nitrile | Dimethyl Sulfoxide | Aldehyde

We have described a one pot multicomponent approach to the synthesis of oxidized amides from nitriles. In consideration of the numerous methods that are available for nitrile preparation, the capacity for variation of the nucleophile, electrophile, and nitrile components, the inherent utility of the products as subunits of numerous biologically active compounds, and the ability to employ the products as starting materials in stereoselective transformations, this process is well-suited for applications in target- and diversity oriented synthesis.

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