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

A novel methodology for the deprotonation of a methyl group on silicon has been developed. This newly developed cr-lithiation protocol is based on the intramolecular pyridyl group coordination to stabilize the a-silyl carbani on together with the inherent silicon a effect. It was found that the depro tonation (t-BuLi/Et2O/-78 degreesC) occurs with 2-pyridyltrimethylsilane bu t not with other related silanes such as phenyltrimethylsilane, 3-pyridyltr imethylsilane, and 4-pyridyltrimethylsilane. It seems that this deprotonati on proceeded through the agency of the complex-induced proximity effect (CI PE) of a 2-pyridyl group on silicon. H-1 NMR analysis of (2-pyridyldimethyl silyl)methyllithium revealed the intramolecular coordination of a pyridyl g roup to lithium. ( 2-Pyridyldimethylsilyl)-methyllithium was found to react with chlorosilanes, hydrosilanes, chlorostannanes, bromine, iodine, organi c bromides, aldehydes, and ketones in good to excellent yields. The resulta nt adducts were further oxidized with H2O2/KF to give the corresponding alc ohols in excellent yields. Thus, this two-step transformation provides an e fficient method for the nucleophilic hydroxymethylation.