A study on the BF3 directed lithiation of 3-chloro- and 3-bromopyridine

The BF3-directed lithiation of 3-chloro- and 3-bromopyridine (1a and 1b, espectively) has been investigated. The reactions of 3-chloro- or 3-bromopyridine-BF3 adduct with LDA (1.3/1.1 equiv) followed by quenching with benzaldehyde or iodine exclusively gave the C-2 substituted products. However, when 2.2 equiv of LDA and dimethyl disulfide was used, a C-6 substituted product was obtained. Dilithiation of 1a and 1b has been studied with and without the involvement of BF3 complexation. The role of Li...F(BF3) interactions has been investigated by experimental and DFT calculations. (C) 2013 Elsevier Ltd. All rights reserved.