TMSCH_2Li and TMSCH_2Li-LiDMAE: Efficient Reagents for Noncryogenic Halogen—Lithium Exchange in Bromopyridines

摘要

TMSCH_2Li and TMSCH_2Li-LiDMAE have been used efficiently for bromine—lithium exchange in 2-bromo-, 3-bromo-, and 2,5-dibromopyridines under noncryogenic conditions, while low temperatures (—78 to —100℃) are always needed with n-BuLi. The aminoalkoxide LiDMAE induced a remarkable C-2 selectivity with 2,5-dibromopyridines in toluene at 0℃, which was unprecedented at such a temperature. The lithiopyridines were successfully reacted with electrophiles also under noncryogenic conditions giving the expected adducts in good yields.