Controlled Anion Migrations with a Mixed Metal Li/K-TMP Amide: General Application to Benzylic Metalations

Abstract

A general method is described for benzylic metalation of o-, m-, and p-substituted toluenes using a mixed metal amide base generated from BuLi/KOtBu/TMP at -78 °C in THF. The excellent selectivity achieved can be rationalized by the ability of the mixed metal amide base to facilitate an anion migration from the kinetic (o-aryl) to the benzylic metalation site. Remarkably, this controlled anion migration is achievable with catalytic amounts of TMP at -78 °C.

Enantioselective Synthesis of Benzyl tert‐Butyl Sulfoxides

“…Table 2 shows that one, two, or three alkoxy substituents, needed for application to lignan syntheses, were tolerated. The yields for the ortho ‐ and meta ‐substituted compounds are very similar to those found by O'Shea using different electrophiles,31 and in addition, these results show that acceptable yields can be obtained with an alkoxy group in the para position. It is not surprising that the presence of electron‐withdrawing substituents facilitated the deprotonation and resulted in good yields of sulfoxides 4h and 4i .…”

“…Superbasic mixtures of organolithium derivatives and/or lithium dialkylamides together with alkali metal alkoxides can be used for the α‐lithiation of a broad range of toluene derivatives 30. Recently, O'Shea and co‐workers used a superbasic mixture formedfrom BuLi, t BuOK, and 2,2,6,6‐tetramethylpiperidine (TMPH),31 and we adopted a similar procedure. We found that the benzyllithium derivatives generated in this way do react with the thiosulfinate 1 , but attack occurs at both sulfur atoms (Scheme ).…”

Developing a Hetero‐Alkali‐Metal Chemistry of 2,2,6,6‐Tetramethylpiperidide (TMP): Stoichiometric and Structural Diversity within a Series of Lithium/Sodium, Lithium/Potassium and Sodium/Potassium TMP Compounds

“…Surprisingly, there appears to have been no progress made in trying to merge ideas from each era, that is in constructing multicomponent TMP complexes8 based on mixed alkali-metal–alkali-metal pairings, a fact made all the more perplexing because hetero-alkali-metal imide,9 alkoxide,10 primary amide,11 heteroanionic alkoxide/primary amide12 and other secondary amide13 complexes have all received attention. The excellent recent studies of O’Shea et al have implicated TMP in a hetero-alkali-metal base for performing selective vinyl14 and alkyl/aryl15 deprotonation in a series of substituted toluenes, albeit using a heteroanionic alkyl/alkoxide/amide base. The empty file on hetero-(alkali-metal)–TMP chemistry is all the more extraordinary given the comprehensive dossier amassed for LiTMP16 (and to a much lesser extent for NaTMP17) and the fact that 20 years have passed since Williard and Nichols established a hetero-(alkali-metal) chemistry of HMDS18 (HMDS=1,1,1,3,3,3-hexamethyldisilazide), another utility amide though a much less powerful base than LiTMP.…”

Zur Metallierung von Benzol und Toluol durch die Schlosser‐Base: ein superbasischer Li2K4‐Cluster unter Beteiligung von PhK, PhLi und tBuOLi

“…[7] Die Handhabung von nBuLi/tBuOK in THF erlaubt die homogene Reaktionsführung mit hoher Chemoselektivität, im Gegensatz zu aliphatischen Lçsungsmitteln, in denen die Mischung eine schlechte Lçslichkeit aufweist. [2] Im Anschluss an unsere Studien zur Metallierung funktionalisierter Arene mit der Schlosser-Base [8] und gemischten Li/K-Amiden [9] untersuchten wir die Deprotonierung der unsubstituierten Arene Benzol und Toluol durch die bimetallische Superbase.…”

“…Ausgewählte Bindungslängen () und -winkel (8): C1-K1' 3.485(4), C4-Li1 ' 2.274(8), C4-K1 2.867(5), C4-K2 3.030(4), C10-Li1 2.494(8), C10-K1 3.442(4), C10-K2 3.145(2), C11-K2' 3.353(5), C14-Li1 2.268 (7), C14-K2 3.092(4), C15-K2' 3.229(4), K1-O1 2.731(2), K1-O2 2.625(6), K2-O4 2.729(3), K2-O3 2.722(4), Li1-O1 1.950 (7), Li'-C4-K1 69.9(2), Li'-C4-K2 68.4(3), K1-C4-K2 114.2(2), Li'-C10-Li 73.3(3), Li-C10-K2 138.0(2), Li-C10-K2' 64.7 (2). nen einen viergliedrigen Ring mit deutlich verlängerten C-Li-Bindungen von 2.494 (8) auf. [10] Das zentrale Motiv ist von einem verzerrten achtgliedrigen Ring aus den vier Phenylkaliumeinheiten umgeben.…”