Organolithium compounds formation, mechanism

Elimination to yield alkenes can be induced thermally or by treatment with acids or bases (for one possible mechanism, see Figure 3.39) [138,206]. Less common thermal demetallations include the thermolysis of arylmethyloxy(phenyl)carbene complexes, which can lead to the formation of aryl-substituted acetophenones [276]. Further, (difluoroboroxy)carbene complexes of molybdenum, which can be prepared by treating molybdenum hexacarbonyl with an organolithium compound and then with boron trifluoride etherate at -60 °C, decompose at room temperature to yield acyl radicals [277]. 

Recently a novel approach to the synthesis of telluranthrene has been suggested (91 KGS 1203) this employs a reaction between poly (o-phenylene)ditelluride and butyllithium. The assumed mechanism of formation of telluranthrene 92 (M = Te) is founded on the known ability of the Te—C (87AG1221) and Te—Te (63CB247) bonds to cleave under the action of organolithium compounds. One of the products of this cleavage, o-dilithiobenzene, reacts with poly(o-phenylene)ditelluride affording tellurantrene in approximately 30% yield. 

In covalent organolithium compounds and covalent Grignard reagents neither the lithium nor the magnesium possesses a valence electron octet. This is energetically disadvantageous. In principle, the same mechanism can be used to stabilize these metals that monomeric boranes BH3 n Rb use to attain a valence electron octet at the boron atom (Section 3.3.3) the formation either of oligomers or, with suitable electron pair donors, of Lewis acid/Lewis base complexes. 

It was shown as early as in Ziegler s classical work [Zi 29, Zi 30] that organolithium compounds were much more reactive in diethyl ether than in solutions prepared with hydrocarbons. This fact has since been confirmed by a number of workers [Ea 63, Sh 66]. It has also emerged that the solvent alters not only the rate but also the mechanism of the reaction. For example, whereas the reaction between n-butyl lithium and benzyl chloride in n-hexane results in the formation of dibenzyl- and n-pentylbenzene, in tetrahydrofuran about 20% trans-stilbene is also obtained, in addition to the former two products [Ho 66]. 

For the formation of 7, a change from the conventional SNAr mechanism (cf. p. 353) to a radical SET process with successive dimerization is likely to be responsible [220], Organolithium compounds and CH-acidic compounds add to acridine at the 9-position to give 9,10-dihydroacridines. For instance, with nitromethane in basic medium, the adduct 8 is formed, whereas phenyhnethylsulfone yields 9-methylacridine, since the adduct 9 eliminates phenylsulfinic acid ... 

Another route to carbon-carbon bond formation is via iodine-induced rearrangement of adducts of trisubstituted boron compounds and organolithium reagents. The adducts of trialkylboranes with lithium acetylides give an akylated acetylene. The mechanism involves electrophilic attack by iodine on the acetylenic... 

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