10th international symposium on the synthesis and applications of isotopes and isotopically labelled compounds-synthesis of compounds labelled with long-lived isotopes Session 17, Thursday, June 18, 2009
Lithiation of 2-Chloro- and 2-Methoxypyridine with Lithium Dialkylamides: Initial Ortho-Direction or Subsequent Lithium Ortho-Stabilization?
作者:Philippe Gros、Sabine Choppin、Yves Fort
DOI:10.1021/jo026559u
日期:2003.3.1
The lithiation pathway of 2-chloro and 2-methoxypyridine with LDA and LTMP has been investigated using deuterated probes. The availability of both H-6 and H-3 protons on the pyridine nucleus was found to be critical to ensure complete C-3 lithiation. We thus concluded that the C-3 lithiation was not a straightforward process. A mechanism involving precomplexation of lithium dialkylamides near the H-6 proton and formation of a 3,6-dilithio pyridine intermediate is proposed.
Lithiation of 2-Heterosubstituted Pyridines with BuLi−LiDMAE: Evidence for Regiospecificity at C-6
作者:Philippe Gros、Sabine Choppin、Julien Mathieu、Yves Fort
DOI:10.1021/jo015855o
日期:2002.1.1
The determination of the initial deprotonation site of 2-chloro- and 2-methoxypyridine during reaction with BuLi-LiDMAE has been investigated. A series of experiments on deuterated regioisomers revealed a direct lithiation at C-6 excluding a potential first classical ortholithiation and lithium equilibration in the reaction medium. These results suggested that the formation of lithium aggregates at the neighboring of the pyridinic nitrogen atom favored BuLi delivery at C-6 as well as 6-lithio intermediate stabilization.
Unusual C-6 Lithiation of 2-Chloropyridine-Mediated by BuLi−Me<sub>2</sub>N(CH<sub>2</sub>)<sub>2</sub>OLi. New Access to 6-Functional-2-chloropyridines and Chloro-bis-heterocycles
作者:Sabine Choppin、Philippe Gros、Yves Fort
DOI:10.1021/ol005538o
日期:2000.3.1
the loss of chlorine atom while exclusive directed ortho metalation is obtained using LDA. Herein it is shown that the BuLi-Me(2)N(CH(2))(2)OLi (BuLi-LiDMAE) superbase promotes an unprecedented regioselective C-6 lithiation. The method was successfully applied to the preparation of potentially useful chlorinated pyridinic and bis-heterocyclic synthons.