The deceptively simple "cross-coupling" reactions Alk(2)C=CA-Cl + RLi --> Alk(2)C=CA-R + LiCl (A = H, D, or Cl) occur via an alkylidenecarbenoid chain mechanism in three steps without a transition metal catalyst. In the initiating step 1, the sterically shielded 2-(chloromethylidene)-1,1,3,3-tetramethylindans 2a-c (Alk(2)C=CA-Cl) generate a Cl,Li-alkylidenecarbenoid (Alk(2)C=CLi-Cl, 6) through the transfer of atom A to RLi (methyllithium, n-butyllithium, or aryllithium). The chain cycle consists of the following two steps: (i) A fast vinylic substitution reaction of these RLi at carbenoid 6 (step 2) with formation of the chain carrier Alk(2)C=CLi-R (8), and (ii) a rate-limiting transfer of atom A (step 3) from reagent 2 to the chain carrier 8 with formation of the product Alk(2)C=CA-R (4) and with regeneration of carbenoid 6. This chain propagation step 3 was sufficiently slow to allow steady-state concentrations of Alk(2)C=CLi-Aryl to be observed (by NMR) with RLi = C6H5Li (in Et2O) and with 4-(Me3Si)C6H4Li (in t-BuOMe), whereas these chain processes were much faster in THF solution. PhC[triple bond]CLi cannot perform step 1, but its carbenoid chain processes with reagents 2a and 2c may be started with MeLi, whereafter LiC[triple bond]CPh reacts faster than MeLi in the product-determining step 2 to generate the chain carrier Alk(2)C=CLi-C[triple bond]CPh (8g), which completes its chain cycle through the slower step 3. The sterically congested products were formed with surprising ease even with RLi as bulky as 2,6-dimethylphenyllithium and 2,4,6-tri-tert-butylphenyllithium.

Tetrahydrofuran solutions of the products formed in LiCl-mediated zinc insertion reactions into various organic halides RHal were analyzed by anion-mode electrospray ionization (ESI) mass spectrometry. In all cases, organozincate anions were observed. The reactions with RHal, Hal ) Br and I, yielded predominantly mononuclear complexes, such as ZnRHal 2 and ZnRHalCl -, whereas for the reaction with benzylchloride abundant polynuclear organozincates, such as Zn 2 Bn 2 Cl 3 and Zn 3 Bn 3 Cl 4 -, were detected. The equilibria governing the stoichiometry and aggregation state of these complexes appear to be mainly controlled by the nature of the halide ions present in solution. It seems likely that the formation of organozincate complexes also changes the reactivity of the organozinc species, thus offering a rationale for the recently found pronounced effect of LiCl in organozinc chemistry. Additional preliminary studies suggest that organozincate anions as well as organozinc cations may moreover form in the absence of LiCl.

Electrospray ionization (ESI) of mixtures of organolithium compounds and zinc chloride in tetrahydrofuran produced manifold mono-and polynuclear organozincate anions. Formation of the latter is strongly favored by the incorporation of chloride ligands, which apparently adopt bridging binding modes. Analysis of Li n Bu/ZnCl 2 solutions at different concentrations showed that the relative ESI signal intensities for anions in different aggregation states closely correlate with their expected equilibria in solution. Moreover, the uni-and bimolecular gas-phase reactivity of the mass-selected anionic organozincates was studied. Upon collision-induced dissociation, most of these complexes lose a neutral metal fragment, and only the tributylzincates ZnBu 3 react by elimination of alkenes. The tributylzincate complexes were also found to undergo ion-molecule reactions with formic acid. The relative rates for these proton-transfer processes decrease in the series Zn n Bu 3 -, Zn s Bu 3 -, and Zn t Bu 3 -, and they also decrease if the butyl groups are substituted for chloride ligands. These trends fully agree with the known solution-phase chemistry of organozinc compounds.

The title compound is entirely monomeric in THF as the solvent, but its two ortho-diisopropyl substituents (in contrast to two tert-butyl groups) do not suffice to prevent its dimerization in Et 2 O: At −107 °C, the disolvated dimer (43% of the total material in monomeric formula units) was accompanied by the disolvated (15%) and the trisolvated monomers (42%). Increasing temperatures reduced trisolvation by Et 2 O to disolvation and diminished also the combined monomer portions (10% at +25 °C); hence, dimerization in Et 2 O is endothermic (+3.1 kcal mol −1 ) but favored by a strongly positive entropy. Microsolvation by only one tert-butyl methyl ether (t-BuOMe) ligand per Li cation of the dimer in t-BuOMe solution was discovered through NMR integration; this disolvated dimer was also observed in cyclopentane as the solvent from −85 to at least +25 °C (hence, no monomer, no higher aggregate). Aryl rotations about the (partial) single bond to the carbanionic center C-α were assessed from the temperatures of NMR signal coalescences of the diastereotopic methyls in an isopropyl group: they are slowest in THF as the solvent because the monomer is then always trisolvated, and delocalization of the negative charge from C-α into the aromatic π-system is therefore most efficient (hence, more rotation-resistant). Microsolvation controls also the cis/trans sp 2 -stereoinversion, which is faster in THF than in the other three solvents because only one additional THF ligand must temporarily be immobilized (performing THF catalysis) on the way to the tetrasolvated, ionic transition state that involves rehybridization (close to sp) of C-α (pseudoactivation entropy ΔS ψ ⧧ = −23.6 cal mol −1 K −1 ). Most of the pertaining microsolvation numbers became available through their empirical relationship with the measured one-bond 13 C− 6 Li NMR coupling constants.

The marine natural product flustramine C from the bryozoan Flustra foliacea was synthesized in five steps and 38% yield starting from Nb-methyltryptamine. The key step is the biomimetic oxidation of the natural product deformylflustrabromine causing selective 1,2-rearrangement of the inverse prenyl group. By 1H,15N HMBC experiments, it is unambiguously shown that the reaction with t-BuOCl commences with chlorination of the side chain nitrogen. Deformylflustrabromine itself was synthesized via Danishefsky inverse prenylation. [reaction: see text].