An.. ylide mechanism" is proposed for the carbodesilylation of 2-(trimethylsily1) pyridines with benzaldehyde. In contrast, 3-and 4-(trimethylsilyl) pyridines, react only in the presence of a base catalyst via pyridyl anions with electrophiles. The rates of the uncatalyzed carbodesilylation reactions of 4-substituted 2-(trimethylsily1) pyridines 2 with benzaldehyde correlate very well with the resonance parameters of the substituents &, whereas the rates ...