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An ylide (/ ˈ ɪ l aɪ d /) [1] or ylid (/ ˈ ɪ l ɪ d /) is a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge (usually nitrogen, phosphorus or sulfur), and in which both atoms have full octets of electrons.
Pyridinium refers to the cation [C 5 H 5 NH] +. It is the conjugate acid of pyridine . Many related cations are known involving substituted pyridines, e.g. picolines, lutidines, collidines.
The first reaction is the formation of the N-2,4-dinitrophenyl-pyridinium salt (2). This salt is typically isolated and purified by recrystallization. The formation of the DNP-pyridinium salt. Upon heating a primary amine with the N-2,4-dinitrophenyl-pyridinium salt (2), the addition
Zincke aldehydes, or 5-aminopenta-2,4-dienals, are the product of the reaction of a pyridinium salt with two equivalents of any secondary amine, followed by basic hydrolysis. Using secondary amines (as opposed to primary amines) the Zincke reaction takes on a different shape forming Zincke aldehydes in which the pyridine ring is ring-opened ...
Radicals can propagate (k p) but also terminate (k t). However, persistent radicals (X), as stated above, cannot terminate with each other but only (reversibly) cross-couple with the growing species (k deact). Thus, every act of radical–radical termination is accompanied by the irreversible accumulation of X. Consequently, the concentration ...
Iodonium ylides undergo cycloaddition with alkene acceptors in low yields. [10] In the presence of nucleophiles, substitution of the iodonium group occurs. [11] (9) Reactions with electrophiles yield iodonium salts, which may be quenched in situ by nucleophilic counteranions. In the presence of non-nucleophilic counteranions, the substituted ...
However, the study of azomethine ylides has verified that cycloaddition is also stereospecific with respect to the dipole component. Diastereopure azomethine ylides are generated by electrocyclic ring opening of aziridines, and then rapidly trapped with strong dipolarophiles before bond rotation can take place (see scheme below).
The Kröhnke pyridine synthesis is reaction in organic synthesis between α-pyridinium methyl ketone salts and α, β-unsaturated carbonyl compounds used to generate highly functionalized pyridines. Pyridines occur widely in natural and synthetic products, so there is wide interest in routes for their synthesis.