Nucleophilic addition to chiral pyridinium salts: stereoselective synthesis of (−)-Na-methylervitsine

Electrophile-induced dearomatizing spirocyclization of N-arylisonicotinamides: a route to spirocyclic piperidines

Treatment of N-arylisonicotinamides with trifluoromethanesulfonic anhydride triggers intramolecular nucleophilic attack of the aryl ring on the 4-position of the pyridinium intermediate. The products are spirocyclic dihydropyridines which can be converted to valuable spirocyclic piperidines related to biologically active molecules such as MK-677.

Regio- and Stereoselective Addition of Allylmetal Reagents to Pyridinium−π and Quinolinium−π Complexes

[reaction: see text] Regio- and stereoselective allylation of pyridinium and quinolinium salts was performed by the addition of allylindium and allyltributyltin reagents toward intermediary cation-pi complexes. The reaction with allylindium and allyltributyltin reagents afforded a 1,2-adduct, whereas the addition of a prenylindium reagent gave a 1,4-adduct with good regio- and stereoselectivities. X-ray structural analysis, 1H NMR studies, and DFT calculations elucidated the intermediary cation-pi complex formation with face-to-face orientation.