Adalbert Maercker

6Li, 6Li-COSY ― A new tool for structure determinations of lithium organic compounds in solution

Abstract A homonuclear 6 Li, 6 Li shift correlation experiment has been successfully performed for 3,4-dilithio-2,5-dimethyl-2,4-hexadiene, thereby providing information about the structure of this compound.

Side and consecutive reactions in metallation of alkyl phenyl ethers: I. The reaction of phenetole with ethyllithium

Abstract Two different mechanism become operative in the cleavage of phenetole by ethyllithium. Furthermore the metallated species adds to ethene or undergoes a condensation reaction to yield a biphenyl derivative.

The Reaction of Substituted Vinylsilanes with Lithium Metal

Vinylsilanes are known to react with lithium metal to form either 1,2-dilithioethanes by reduction or 1,4-dilithiobutanes by reductive dimerization. The reaction of the substituted vinylsilanes 3, (Z)-13b, 17b, c, 42b, c, 44, and 51 with lithium has been investigated. Depending on the substituents on the vinylsilane and the solvent employed, several new reaction pathways are observed, which have been proved by independent syntheses of the reactive intermediates (E)-14b, 18d, and 25-27. Thus, besides the known elimination of lithium hydride, either a 1,4-proton shift of 25 to 26 or a Grovenstein-Zimmerman rearrangement of 45 to 47 can occur as follow-up reactions. Furthermore, two different types of dimerization of the silyl-substituted vinyllithium compounds have been identified. Either the vinyllithium compound 18d adds to the starting vinylsilane leading to the monolithiumorganic species 41, or lithium metal catalyzed dimerization to the 1,4-dilithio-2-butene derivative 49 takes place, which is without precedence.

Controlled Rearrangement of 2,3-Dilithio-1,3-butadienes to 2,5-Dilithio-1,3-butadienes: Synthesis of 2-Isopropylidene-2,5-dihydrosilols

3,4-Dilithio-2,5-dimethyl-2,4-hexadiene (4a) rearranges to the cross-conjugated 2,5-dimethylhexadienediyl dianion 11a. A mechanistic investigation proves the intermolecularity of this rearrangement, which is also observed when starting from 4b. The 3-lithio-2,5-dimethylhexadienyl anion 10a with one vinyllithium and one allyllithium group, is a true intermediate in this rearrangement, its synthetic potential is employed in the reaction with dichlorosilanes to form 2-isopropylidene-2,5-dihydrosilols 8.

Mechanismus der Reduktion von Diphenylacetylen mit metallischem Lithium

In einer Reaktion nullter Ordnung wird cis-Dilithiostilben 1, das aus Diphenylacetylen und Lithiummetall in Diethylether zuganglich ist, in das trans-Isomer 2 umgelagert. Monolithiiertes Stilben fungiert dabei als Katalysator.

NMR studies of dilithiostyrenes: aggregation, NMR parameters, and DFT calculations for (E)-1-Lithio-2-(o-lithiophenyl)-1-trimethylsilylethene†‡

The dilithio compound (E)‐1‐lithio‐2‐(o‐lithiophenyl)‐1‐trimethylsilylethene (5) was synthesized from 2‐trimethylsilylbenzo‐[b]tellurophene (6) with lithium‐6 and a detailed analysis of its 1H, 6Li, 13C, and 29Si NMR spectra showed 5 to form a dimer 52 in tetrahydrofuran and diethylether, while addition of tetramethylethylenediamine stabilizes a monomer 51. A monomer–dimer equilibrium exists with K at 230 K = 1.25 and ΔG230o  = −0.43 kJ mol−1. Homonuclear 6Li,6Li coupling of 0.25 ± 0.07 Hz in the dimer was detected by a 1D‐6Li,6Li INADEQUATE experiment, and scalar 6Li,13C coupling constants were obtained from 13C satellites in the 6Li spectrum, from 13C multiplet simulation and 6Li,13C‐HMQC spectra. In addition, structures and coupling constants of 51 and 52 were calculated by density functional theory (DFT) methods. It was found that the magnitude of the 6Li,13C spin–spin interactions shows an inverse correlation with the C‐Li bond lengths. The intra‐aggregate exchange in the dimer, caused by 180° rotation of one monomer unit within the solvent cage, was studied by 6Li DNMR and line shape analysis and yielded ΔG298≠  = 60 ± 3 kJ mol−1; ΔH≠ = 84 ± 3 kJ mol−1; ΔS≠ = 80 ± 3 J mol−1 K−1 for this process. Copyright

On the mechanism of bibenzyl formation by deoxidation/reduction of aromatic species with lithium 4,4′-di-t-butylbiphenyl radical anion - a correction

Abstract In the reaction of benzil with lithium in the presence of 4,4′-dit-butylbiphenyl (DBB)trans-stilbene4 and dilithiobibenzyl5 are intermediates instead of the reported tetralithiobibenzyl2.