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With water-soluble derivatives of ethyl cyanohydroxyiminoacetate (glyceroacetonide-oxyma) as additive and DIC as coupling reagent even in weakly basic aqueous solutions the linking of protected amino acids to oligopeptides is possible with a yield of 95% and a diastereomeric excess of> 99% using the model substances Z-L-Phg-OH and L-H-Pro-NH 2 ...
In one important reaction type, a main group organometallic compound of the type R-M (where R = organic group, M = main group centre metal atom) reacts with an organic halide of the type R'-X with formation of a new carbon-carbon bond in the product R-R'. The most common type of coupling reaction is the cross coupling reaction. [1] [2] [3]
The Seyferth–Gilbert homologation is a chemical reaction of an aryl ketone 1 (or aldehyde) with dimethyl (diazomethyl)phosphonate 2 and potassium tert-butoxide to give substituted alkynes 3. [1] [2] Dimethyl (diazomethyl)phosphonate 2 is often called the Seyferth–Gilbert reagent. [3] The Seyferth–Gilbert homologation
To illustrate the impact of suboptimal coupling yields for a given synthesis, consider the case where each coupling step were to have at least 99% yield: this would result in a 77% overall crude yield for a 26-amino acid peptide (assuming 100% yield in each deprotection); if each coupling were 95% efficient, the overall yield would be 25%.
Cross-couplings are a subset of the more general coupling reactions. Often cross-coupling reactions require metal catalysts. One important reaction type is this: R−M + R'−X → R−R' + MX (R, R' = organic fragments, usually aryl; M = main group center such as Li or MgX; X = halide) These reactions are used to form carbon–carbon bonds but ...
The McMurry reaction of benzophenone. The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to form an alkene using a titanium chloride compound such as titanium(III) chloride and a reducing agent.
Although the Fukuyama cross-coupling reaction has been widely used in natural product synthesis, the reaction mechanism remains unclear.Various catalysts have been shown to promote reactivity, including Pd/C, Pd(OH) 2 /C, Pd(OAc) 2, PdCl 2, NiCl 2, Ni(acac) 2, etc. [2] The proposed catalytic cycle using Pd(OH) 2 /C (Pearlman’s catalyst) features the in situ generation of active Pd/C by ...
Acyloin condensation is a reductive coupling of two carboxylic esters using impure metallic sodium to yield an α-hydroxyketone, also known as an acyloin. [1] [2] [3] The acyloin condensation. The reaction is most successful when R is aliphatic and saturated, and typically performed with a silyl chloride reactant to trap the product as a ...