The Origin of Regioselectivity in an Allenyllithium Reagent

Selective Meta‐Deprotonation of Toluene by Using Alkali‐Metal‐Mediated Magnesiation

“…A 1 H NMR spectrum of the filtrate showed that 1 had converted essentially quantitatively into trimethyl meta-tolylsilane, as established by comparison with an authentic sample of trimethyl metatolylsilane. [16] This promising result confirms that 1 should be an excellent precursor to meta-substituted tolyl compounds.…”

“…However, meta-deprotonation has also been observed in tmeda-free solutions in the synthesis of the dideprotonated complex [Na 4 Mg 2 (C 6 H 3 CH 3 )(tmp) 6 ], so the tmeda-free models 1 A-1 D probably provide a reasonable guide to the experimental reaction. Noting that conventional magnesium bases are generally too weak to metalate toluene, this new synergic mixed-metal methodology that opens a direct route to metasubstituted toluenes, [15,16] is perhaps best regarded as alkalimetal-mediated magnesiation, a new form of magnesiation with greatly enhanced basic powers. [17] To test its ability to be intercepted by electrophiles, 1 was treated with three molar equivalents of trimethylsilyl triflate in [D 6 ]benzene solution.…”

Selective Meta‐Deprotonation of Toluene by Using Alkali‐Metal‐Mediated Magnesiation

“…However, meta ‐deprotonation has also been observed in tmeda‐free solutions in the synthesis of the dideprotonated complex [Na 4 Mg 2 (C 6 H 3 CH 3 )(tmp) 6 ], so the tmeda‐free models 1 A – 1 D probably provide a reasonable guide to the experimental reaction. Noting that conventional magnesium bases are generally too weak to metalate toluene, this new synergic mixed‐metal methodology that opens a direct route to meta ‐substituted toluenes,15, 16 is perhaps best regarded as alkali‐metal‐mediated magnesiation, a new form of magnesiation with greatly enhanced basic powers 17…”

Polylithiumorganic compounds

“…This kind of tautomerism has been observed, in the case of a dilithiumorganic compound, in the solid-state structures of dilithium 1,2-diphenylbenzocyclobutadienediide, where the lithium atoms are at different positions in the same molecule. [10] We have, however, shown that for unsymmetrically substituted 2,3-dilithiobutadienes (which would be better named 3,4-dilithio-1,2-butadienes Ϫ with the corresponding structure 6) the product mixtures obtained upon reaction with various electrophiles are mainly determined by the nature of the electrophile. [8a] More recently, thorough low-temperature NMR studies by Reich and co-workers on simple allenyl-/ propargyllithium compounds, have established that for special cases, a real equilibrium exists between tautomeric intermediates in solution.…”