Cross-dehydrogenative coupling pyridine

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. 

Metal-mediated Reaction. The o -position of this inner salt can undergo dehydrogenative cross-coupling with terminal aUcynes, such as phenylacetylene, under Cu-mediated reaction conditions. The a-alkynyl derivative readily cyclizes in situ with the loss of the Ts group to afford 2-phenylpyrazolo[ l,5-a]pyridine in a 22% yield. This inner salt does not work as well as the analogous l-(benzoylamino)pyridinium inner salt in this reaction. ... 

A dehydrogenative cross-coupling between pyridines or five-membered heteroarenes with secondary phosphites has recently been developed (Schemes 4.251 and 4.252) [406]. The approach used silver nitrate as the promoter and K S Og as an oxidant. When the... 

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