ortho-Lithiations Reassessed: the Advantages of Deficiency Catalysis in Hydrocarbon Media
作者:D. W. Slocum、Thomas K. Reinscheld、Christopher B. White、Michael D. Timmons、Philip A. Shelton、Matthew G. Slocum、Rebecca D. Sandlin、Erica G. Holland、Damir Kusmic、John A. Jennings、Kristen C. Tekin、Quang Nguyen、Steven J. Bush、Julia M. Keller、Paul E. Whitley
DOI:10.1021/om301120e
日期:2013.3.25
Hydrocarbon media based metalation procedures involving "deficiency catalysis" are described for the ortho-lithiation of anisole (A), p-chloroanisole (p-ClA), o-, m-, p-methylanisoles (o-, m-, p-MA), the three dimethoxybenzenes (DMB's), dimethylaniline (DMA), dimethybenzylamine (DMBA), m-methoxydimethylaniline (m-MeODM.A), and tetramethyl-p-phenylenediamine (p-TMPDA). These procedures involve certain mechanistic considerations, which must be fine-tuned to maximize the extent of metalation (EoM). Our working hypothesis is that a controlled deoligomerization of the n-BuLi hexamer found in hydrocarbon media will afford a "sweet spot" of deoligomerization such that a maximally efficient metalation medium can be formed. In many eases, a substoichiometric ratio of equivalent TMEDA to n-BuLi is 0.1-0.2:1.0, but certain substrates suffer multiple sites of metalation under these conditions, so different promoted hydrocarbon media systems incorporating measured equivalents of an ether have been formulated. This paper represents the summary of our successful efforts to render ortho-lithiations safer, greener, and more atom-economical by use of hydrocarbon solvent media. EoM's of 11 of the 12 substrates under these atom-economical conditions range from 87 to 97%.