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The synthetically most useful reaction of the nitrile ylides is the 1,3-dipolar cycloaddition to dipolarophiles: with electron-deficient alkenes, good yields of pyrrolines are obtained. Alkynes, carbonyl compounds, imines and azirines can also act as dipolarophile.
However, a few examples exist of a stepwise mechanism for the catalyst-free 1,3-dipolar cycloaddition reactions of thiocarbonyl ylides, [6] and nitrile oxides [7] The generic mechanism of a 1,3-dipolar cycloaddition between a dipole and a dipolarophile to give a five-membered heterocycle, through a six-electron transition state.
A phosphonium ylide can be prepared rather straightforwardly. Typically, triphenylphosphine is allowed to react with an alkyl halide in a mechanism analogous to that of an S N 2 reaction. This quaternization forms an alkyltriphenylphosphonium salt, which can be isolated or treated in situ with a strong base (in this case, butyllithium) to form ...
In organic chemistry, a 1,3-dipolar compound or 1,3-dipole is a dipolar compound with delocalized electrons and a separation of charge over three atoms.They are reactants in 1,3-dipolar cycloadditions.
The reaction is assisted by the copper, which, when coordinated with the acetylide lowers the pKa of the alkyne C-H by up to 9.8 units. Thus under certain conditions, the reaction may be carried out even in the absence of a base. In the uncatalysed reaction the alkyne remains a poor electrophile. Thus high energy barriers lead to slow reaction ...
The former is called the ylide form and the latter is called the phosphorane form, ... Wittig reaction in Organic Syntheses, Coll. Vol. 10, p. 703 (2004); Vol. 75, ...
The nitrone-olefin (3+2) cycloaddition reaction is the combination of a nitrone with an alkene or alkyne to generate an isoxazoline or isoxazolidine via a (3+2) cycloaddition process. [1] This reaction is a 1,3-dipolar cycloaddition, in which the nitrone acts as the 1,3-dipole, and the alkene or alkyne as the dipolarophile.
The Ritter reaction (sometimes called the Ritter amidation) is a chemical reaction that transforms a nitrile into an N-alkyl amide using various electrophilic alkylating reagents. The original reaction formed the alkylating agent using an alkene in the presence of a strong acid. [1] [2] [3] [4]