Hetarynes

Generation, Characterization, and Reactivity of the Transition Metal−o-Benzyne Analog of Pyrazine (Fe+−2,3-Didehydropyrazine) in the Gas Phase: An Experimental and Theoretical Study

“…In comparison to o -benzyne, the hetarynes are considerably more complex and, potentially, more interesting. A number of hetarynes have been studied in the past few decades. , Hetarynes are believed to be important intermediates in nucleophilic substitutions on heterocyclic aryl halides. − Principal attention has focused on the 1,2-didehydroaromatics derived from nitrogen heterocyclics such as pyridine, quinoline, isoquinoline, and the various diazines. ,− Didehydropyrazine, on the other hand, has received relatively little attention. As the heterocyclic analogue of o -benzyne (1,2-dehydrobenzene), 2,3-didehydropyrazine ( 1 ) is the only isomer that can be drawn for the didehydropyrazine due to the symmetrical presence of the two nitrogen atoms.…”

Synthetic Organic Reactions Mediated by Sodium Hydride

“…Especially, it is worthy of note that the method enables installation of amine functionality onto the C3 position of pyridines (Scheme 30). Selective C3 amination of pyridines is still challenging: the common nucleophilic aromatic substitution of (pseudo) halopyridines with amine nucleophiles via the stepwise S N Ar (addition elimination) mechanism 32,33 or via the corresponding pyridyne intermediates (elimination addition), 34,35 which have thus far been proven successful only for the C2 and C4 amination due to the inherent nature of the pyridines or pyri- dyne intermediates. This protocol allowed for iterative amination of dimethoxypyridine such as 85 to install two different amine functionality at C3 and C5 position of 87 (Scheme 31).…”

“…22 We became interested in use of our NaH iodide system for chemical reduction of phosphine oxides, with the assumption of production of phosphines. However, unexpectedly, the reaction of triphenylphosphine oxide (32) under the NaH NaI/LiI system afforded dephenylation product, diphenylphosphine oxide (34), that should be formed via protonation of sodium (lithium) phosphinite 33 during the aqueous workup (Scheme 16A). Seyferth earlier reported dephenylative methylation of triphenylphosphine oxide (32) by the treatment with MeLi (Scheme 16B).…”

Density Functional Theory Study of Molecular Structures and Vibrational Spectra of 3,4- and 2,3-Pyridyne

“…Pyridynes (didehydropyridines) have been proposed as intermediates in many organic reactions such as cycloaddition, cine-substitution, and tele-substitution . They are the most studied of all known didehydroheteroarenes. − Yet there was no direct evidence for the existence of pyridyne as an intermediate until 1988 when Nam and Leroi published the first matrix infrared study of the photolysis products of 3,4-pyridinedicarboxylic anhydride . Before this paper was published, only indirect evidence, based on trapping experiments to verify the presence of heteroaryne, was obtained.…”