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hydrochloric acid to make a chloroalkane or conc.
A variety of methods exist to install the cyano group on organic molecules. Related to the metal-catalyzed method described in this article is the palladium-catalyzed cross-coupling of vinyl halides and cyanide (Eq. 16). Hydrogen cyanide is not neeeded for this method and it is completely stereospecific; however, the vinyl halide substrates used in these reactions are more complex than simple alkenes and alkynes.
Reactions are usually straightforward (SEAr) and you will have met most of them before. Synthesis is simplified because the nature of the starting materials is usually clear. Thus, most reactions correspond to the following disconnection:
hydrobromic acid to make a bromoalkane.
– the process of writing one functional group for another to help synthetic planning and to help disconnection. Note, there must be a good reaction in the reverse (forward!) direction.
Review and extend CCBFR from 1C1Y, in particular:
Aldol and Claisen condensations
Alkylation of -keto esters (RCHOCH2CO2R’)
aq) and HBr(g/non-polar solvent)] to form halogenoalkanes
Nucleophilic addition of cyanide to alkyl halides is an alternative method for the preparation of saturated nitriles. Phase-transfer catalysis has been used in this context.
Asymmetric hydrocyanation reactions involving nickel(0) catalysts most often employ chiral, chelating bis-triarylphosphite ligands. Strained alkenes may be hydrocyanated to yield products with moderate enantioselectivity. The example in Eq. 12 highlights the use of acetone cyanohydrin as an alternative source of HCN.
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sulphuric acid to alkene now on separate page
Trimethylsilyl cyanide is less toxic than hydrogen cyanide, and may be used successfully in metal-catalyzed additions to alkynes. For reactions with terminal alkynes completely site selectivity is observed (the internal nitrile is the observed product). Nearly complete stereoselectivity is observed as well (Eq. 11).
1. To introduce basic concepts of organic synthesis:
At elevated temperatures, unactivated terminal alkenes may be hydrocyanated by nickel(0)-bisphosphine complexes in the presence of a Lewis acid. Aluminum trichloride and a number of other Lewis acids provide the anti-Markovnikov addition selectively (Eq. 7). Rigid, chelating phosphine ligands with bite angles in excess of 100 degrees (such as Xantphos) are needed for reactions with isolated alkenes.
Carboxylic acid synthesis by oxidation of alkenes or …
Evidence accumulated to date suggests that removing electron density from the nickel center increases the rate of reductive elimination relative to β-hydride elimination, which re-forms the starting alkene. Furthermore, when a chiral ligand is used, the effect is greater for one diastereomeric pathway than the other, resulting in increased enantioselectivity. This electronic effect supplements the steric constraints imposed by the shape of the ligand.
Epoxide synthesis by epoxidation - Organic chemistry
The hydrocyanation of alkenes by nickel(0) complexes proceeds stereospecifically (Eq. 5). Migratory insertion occurs in a fashion and reductive elimination occurs with retention of configuration. Evidence for addition in hydrocyanations of dienes and vinylarenes has also been observed.
Dihydroxylation of alkenes with cold, dilute KMnO4 to …
The nickel-catalyzed hydrocyanation of alkynes is mechanistically similar to the alkene hydrocyanation mechanism described above. Hydrogen and cyanide add across the triple bond in a fashion. When terminal alkynes are employed as substrates, internal nitriles are the major products in the absence of (often important) steric factors. This preference is explained by the greater stability of bonds between nickel and more highly substituted carbons.
Alkene Reactivity - Michigan State University
The use of such enolate anions from carbonyl compounds is fundamental to organic synthesis and you will already have met them as intermediates in the Aldol reaction and Claisen condensation.
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