A study on the BF3-directed lithiation of 2-picoline and 2,3-lutidine

• The BF3-directed mono- and dilithiation of 2-picoline/2,3-lutidine has been studied.
• The results obtained with BF3-aided reaction have been compared with unaided reactions.
• Synthesis of the diiodo derivatives of picolyl/lutidinyl dimers has been provided.

The lithiation of 2-picoline (1a) and 2,3-lutidine (1b) in diethyl ether has been investigated with and without prior complexation with BF3. The reactions of the BF3 adduct of these moieties (2a and 2b) with lithium diisopropylamide (LDA) and subsequent trapping with benzaldehyde or dimethyl disulfide gave products corresponding to exclusive lithiation at the α-methyl carbon. The yields obtained with these reactions were far superior to that obtained with the lithiation of uncomplexed 1a and 1b. The dilithiation of 2a and 2b has also been investigated and a convenient and efficient synthesis of the diiodo derivatives of 1,2-bis(pyridin-2-yl)ethane has been provided.

The reaction of the BF3 adduct of 2-picoline (1a) and 2,3-lutidine (1b) with LDA and subsequent trapping with benzaldehyde or dimethyl disulfide gave products corresponding to exclusive lithiation at the α-methyl carbon. The dilithiation reaction involving iodine as the electrophile exclusively gave the diiodo derivatives of 1,2-bis(pyridin-2-yl)ethane.Figure optionsDownload as PowerPoint slide