Homoleptic zincate-promoted room-temperature halogen-metal exchange of bromopyridines

International audienceHomoleptic lithium tri- and tetraalkyl zincates were reacted with a set of bromopyridines. Efficient and chemoselective bromine-metal exchanges were realized at room temperature with a substoichiometric amount of nBu4ZnLi2*TMEDA reagent (1/3 equiv; TMEDA=N,N,N',N'-tetramethylethylenediamine). This reactivity contrasted with that of tBu4ZnLi2*TMEDA, which was inefficient below one equivalent. DFT calculations allowed us to rationalize the formation of N***Li stabilized polypyridyl zincates in the reaction. The one-pot difunctionalization of dibromopyridines was also realized using the reagent stoichiometrically. The direct creation of C Zn bonds in bromopyridines enabled us to perform efficient Negishi-type cross-couplings