HOMOTRANSMETALLATION DES HALOGENO-3 PYRIDINES BROMEES EN -2 OU -4 PAR LE N-BUTYLLITHIUM. PROPOSITION D'UN NOUVEAU MECANISME DE TELESUBSTITUTION DU BROME.

Article abstract of DOI:10.1016/S0040-4020(01)90605-2

These are new examples of the homotransmetallation reaction.Instead of the ordinary bromo-metal exchange it is possible to obtain selectively from the 2-bromo 3-fluoro or 2-bromo 3-chloro pyridines the 2-bromo 3-halogeno 4-lithio pyridines, which is very interesting for synthetic utility.From the 4-bromo 3-halogeno pyridines, we can see an isomerization with an halogen dance mechanism and we obtain the 5-bromo 3-halogeno 4-lithio pyridines.In the case of the 2-bromo 3-fluoro pyridine we explain a telesubstitution of bromine from 2 to 4 by a transitory homotransmetallation reaction during the Li-Br exchange.