Pyridyl group assisted deprotonation of a methyl group on silicon: Complex induced proximity effect and novel hydroxymethylation

A novel methodology for the deprotonation of a methyl group on silicon has been developed. This newly developed α-lithiation protocol is based on the intramolecular pyridyl group coordination to stabilize the α-silyl carbanion together with the inherent silicon α effect. It was found that the deprotonation (t-BuLi/Et₂O/-78 °C) occurs with 2-pyridyltrimethylsilane but not with other related silanes such as phenyltrimethylsilane, 3-pyridyltrimethylsilane, and 4-pyridyltrimethylsilane. It seems that this deprotonation proceeded through the agency of the complex-induced proximity effect (CIPE) of a 2-pyridyl group on silicon. ¹H NMR analysis of (2-pyridyldimethylsilyl)methyllithium revealed the intramolecular coordination of a pyridyl group to lithium. (2-Pyridyldimethylsilyl)-methyllithium was found to react with chlorosilanes, hydrosilanes, chlorostannanes, bromine, iodine, organic bromides, aldehydes, and ketones in good to excellent yields. The resultant adducts were further oxidized with H₂O₂/KF to give the corresponding alcohols in excellent yields. Thus, this two-step transformation provides an efficient method for the nucleophilic hydroxymethylation.