Aromatic systems ketoximes

Reaction with ketoximes. Ketoximes and an aromatic carboxylic acid react with this system at 0° to form diacylated aromatic amines (equation I). 

A rhodium-catalyzed one-pot synthesis of substituted pyridine derivatives from a,(3-unsaturated ketoximes and alkynes was developed in 2008 by Cheng and coworkers [99], Good yields of the desired pyri-dines can be obtained (Scheme 3.48). The reaction was proposed to proceed via rhodium-catalyzed chelation-assisted activation of the (3—C—H bond of a,(3-unsaturated ketoximes and subsequent reaction with alkynes followed by reductive elimination, intramolecular electro-cyclization, and aromatization to give highly substituted pyridine derivatives finally [100]. Later on, in their further studies, substituted isoquinolines and tetrahydroquinoline derivatives can be prepared by this catalyst system as well [101]. Their reaction mechanism was supported by isolation of the ort/jo-alkenylation products. Here, only asymmetric internal alkynes can be applied. 

The cross-coupling reaction of the ketoxime ester 179 with the alkenylboronic acid leads to the 3-azahexa-l,3,5-triene 181 67t-electrocyclization of the triene 181 affords the 3,4-dihydropyridine 182, whose dehydrogenation by O2 aromatizes to the pyridine 180. Notably, this approach allows flexible control over the substitution pattern of the pyridine system to be synthesized. 

In an attempt to extent the reaction of ketoximes with acetylene affording pyrroles over aldoximes, it has been revealed [4,7,387,388] that oximes of aliphatic, aromatic, and heteroaromatic aldehydes are easily transformed into the corresponding nitriles upon moderate heating (60°C-140°C) in the system KOH/DMSO (Scheme 1.179). 

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