Palladium-catalyzed allylation of 2- and 4-alkylpyridines via N-allyl alkylidene dihydropyridine intermediates

Stability and reactivity of alkylidene dihydropyridines

“…8 Pigge has also used these intermediates in Mizoroki–Heck cyclizations 9 and methylenation with Eschenmoser's salt, 10 and applied them to the synthesis of 1,2,4-triazoles 11 and bis-piperidines. 12 Other methods for functionalization of 2- and 4-heterobenzylic positions of pyridines via transient dearomatization have been reported recently 13–18 but they do not involve the discrete ADHP and do not use chloroformate as the activating agent.…”

Groups 9 and 10 Complexes of C–Donor Ligands Derived from Pyridinium-Stabilized Phosphorus Ylides

“…While these compounds can be formulated as resonance-stabilized zwitterions ( 3 , 4 ), the neutral alkylidene dihydropyridine form ( 5 ) is generally the major resonance contributor. We and others have been exploring metal-catalyzed transformations of alkylidene dihydropyridines (such as Pd-catalyzed Heck and allylation reactions) that, in some cases, are believed to proceed through transiently formed Pd–alkylpyridinium intermediates. − This prompted us to consider the possibility of assembling tractable and isolable metal complexes supported by alkylidene dihydropyridines as C-donor ligands. Precedent for a complex of this type is found in the work of Fürstner et al, who reported the preparation and characterization of the Au­(I) complex 6 from a 2-methylidene dihydropyridine ligand (Scheme B) .…”