Aggregative activation in heterocyclic chemistry. Part 6.† A surprising NH₃ effect during metallation of 2-methoxypyridine with a multimetal complex base: C-3 versus C-6 metallation

Abstract

The new bimetallic complex base prepared from Me₂N(CH₂)₂OH (DMAE), NaNH₂ and BuLi has been found to exhibit a particular behaviour. Thus, the presence of ammonia in these basic aggregates induces the C-3 metallation of 2-methoxypyridine while the base obtained from DMAE, NaH and BuLi promoted, like BuLi–DMAELi, metallation at the C-6 position. A reaction profile showed that both metallated species can be obtained by removing and adding ammonia respectively.

References

1. Ph. Gros, Y. Fort and P. Caubère, J. Chem. Soc., Perkin Trans. 1, 1997, 3071.
2. P. Caubère, Chem. Rev., 1993, 93, 2317 and references cited therein.
3. (a) P. Beak and A. I. Meyers, Acc. Chem. Res., 1986, 19, 356; (b) V. Snieckus, Chem. Rev., 1990, 90, 879.
4. B. Jamart-Grégoire, Y. Fort, M. J. Quirin and P. Caubère, J. Chem. Soc., Chem. Commun., 1992, 19, 1459.
5. (a) P. Caubère, Acc. Chem. Res., 1974, 7, 301; (b) P. Caubère, Top. Curr. Chem., 1978, 73, 50 and references cited therein.
6. (a) L. Lochmann, J. Pospisil, J. Vodnansky, J. Trekoval and D. Lim, Collect. Czech. Chem. Commun., 1965, 30, 2187; (b) L. Lochmann and D. Lim, J. Organomet. Chem., 1973, 50, 9; (c) M. Schlosser, Mod. Synth. Methods, 1992, 6, 227.
7. E. W. Thomas, J. Org. Chem., 1986, 51, 2184.
8. F. Trécourt, M. Mallet, F. Marsais and G. Quéguiner, J. Org. Chem., 1988, 53, 1367.