Breaking the Aromaticity Trap: N -Silylation-Induced Formation of Stable 2,3-Dihydro-4-dialkylaminopyridin-1-iums

High Resolution Image Download MS PowerPoint Slide The reactivity of pyridines toward organolithium reagents is dominated by the nucleophilic addition to the C2 position, leading to the formation of labile 1,2-dihydropyridines that readily rearomatize. Herein, we report an unexpected deviation from this classical pathway. Trimethylsilylation of 4-dialkylaminopyridine steers their reaction with alkyl lithium reagents ( n -BuLi, s -BuLi, t -BuLi) toward the formation of 2,3-dihydro-4-dialkylaminopyridin-1-iums, isolated as air-stable triflates, which are remarkably resistant to oxidation and deprotonation. This stability is attributed to pronounced orbital interactions and charge delocalization between the NR 2 group and the pyridinium core creating a vinylogous amidine structural motif. At the same time, triisopropylsilylation completely suppresses nucleophilic addition, enabling the first case of room-temperature C2 lithiation of the pyridine core. This difference in the reaction pathway originated from a dramatic decrease of the relative steric accessibility of C2(6) pyridine carbon atoms.