- Directed Lithiation of 4-Halopyridines: Chemoselectivity, Regioselectivity and Application to Synthesis
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4-Chloro and 4-fluoropyridines were ortho-lithiated by n-butyllithium-TMEDA chelate or lithium diisopropylamide at low temperature.The resulting 3-lithio 4-halopyridines were reacted with electrophiles which led to various 3,4-disubstituted pyridines.The versatility of this functionalization is enhanced by the 4-halogen reactivity towards nucleophiles such as water, methylate and amines.Some of the 3,4-disubstituted synthons were annelated to naphthyridine, xanthone and coumarin or condensed to Hantzsch-ester or to "chlotrimazol" analogues.Lithiation of 4-fluoropyridine led in one step to 3,4-pyridyne, which was trapped by cycloaddition with furans.
- Marsais, F.,Trecourt, F.,Breant, P.,Queguiner, G.
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