Improving the robustness and scalability of of organolithium and Grignard reactions
05 January 2004
The reaction of an organolithium or an organomagnesium species with an electrophile is a cornerstone of organic synthesis and features in many commercial and development scale manufacturing processes.
Process chemists at Merck have reported* notable improvements in the robustness and scalability of such a reaction, by balancing the high reactivity of the organolithium with the stability of the analogous organomagnesium species via a magnesium "ate" intermediate:
The equivalent organolithium reaction (nBuLi, toluene, -78oC) requires cryogenic conditions and very tight control of stereochemistry. The corresponding Grignard reactions by the Knochel and Queguiner methodologies (iPrMgCl or iPr²Mg, THF, 25oC) give lower yields, are very sluggish and give side products. In contrast, the "ate" approach shown above can tolerate reasonable deviations in stoichiometry and temperature, and it scales up well.
* R.P.Volante (Merck, USA), "Process Development for a Novel Muscarinic M3 Receptor Antagonist", Presentation given at Chiral USA 2003, Chicago, 21/22 October 2003.
[Note that the magnesium "ate" approach was originally described by Oshima et al (Angew. Chem. Int. Ed. Engl., 2000, 39, 2481).]
