Organolithium compounds formation

It has been postulated that the syn TT-ahyl stmcture yields the trans-1 4 polymer, and the anti TT-ahyl stmcture yields the cis-1 4 polymer. Both the syn and anti TT-ahyl stmctures yield 1,2 units. In the formation of 1,2-polybutadiene, it is beheved that the syn TT-ahyl form yields the syndiotactic stmcture, while the anti TT-ahyl form yields the isotactic stmcture. The equihbtium mixture of syn and anti TT-ahyl stmctures yields heterotactic polybutadiene. It has been shown (20—26) that the syndiotactic stereoisomers of 1,2-polybutadiene units can be made with transition-metal catalysts, and the pure 99.99% 1,2-polybutadiene (heterotactic polybutadiene) [26160-98-5] can be made by using organolithium compounds modified with bis-pipetidinoethane (27). At present, the two stereoisomers of 1,2-polybutadiene that are most used commercially are the syndiotactic and the heterotactic stmctures. 

Addition of phenylmagnesium bromide to phthalazin-l(2//)-one or derivatives like 4-phenylphthalazin-l(2/f)-one, 4-phenylphthalazine-l(2/f)-thione and 2-substituted phthalazin-l(2//)-ones results in the formation of 1,4-diphenylphthalazines, while addition of organolithium compounds to phthalazin-l(2/f)-one gives the 4-substituted derivative. 

A more promising procedure for the formation of alkenes from tosylhydrazones is represented by the Shapiro reaction It differs from the Bamford-Stevens reaction by the use of an organolithium compound (e.g. methyl lithium) as a strongly basic reagent ... 

This type of metallic exchange is used much less often than 12-32 and 12-33. It is an equilibrium reaction and is useful only if the equilibrium lies in the desired direction. Usually the goal is to prepare a lithium compound that is not prepared easily in other ways, for example, a vinylic or an allylic lithium, most commonly from an organotin substrate. Examples are the preparation of vinyllithium from phenyl-lithium and tetravinyltin and the formation of a-dialkylamino organolithium compounds from the corresponding organotin compounds ... 

Next to the formation of Grignard reagents, the most important application of this reaction is the conversion of alkyl and aryl halides to organolithium compounds, but it has also been carried out with many other metals, (e.g., Na, Be, Zn, Hg, As, Sb, and Sn). With sodium, the Wurtz reaction (10-93) is an important side reaction. In some cases, where the reaction between a halide and a metal is too slow, an alloy of the metal with potassium or sodium can be used instead. The most important example is the preparation of tetraethyl lead from ethyl bromide and a Pb—Na alloy. 

Scheme 2.3S Formation of exocyclic allenes 103 by intra-molecular SN2 substitution of organolithium compounds.

Since Lewis base additives and basic solvents such as tetrahydrofuran are known to deaggregate polymeric organolithium compounds, (21,23,26) it was postulated that ketone formation would be minimized in the presence of sufficient tetrahydrofuran to effect dissociation of the aggregates. In complete accord with these predictions, it was found that the carbonation of poly(styryl)lithium (eq. 9), poly(isoprenyl)-lithium, and poly(styrene-b-isoprenyl)lithium in a 75/25 mixture (by volume) of benzene and tetrahydrofuran occurs quantitatively to produce the carboxylic acid chain ends (8 ). 

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]. 

Grignard reaction and similar transformations allow C-C bond formation without a palladium catalyst. Grignard reagents and organolithium compounds are very versatile carbanion sources used in the synthesis of acyclic, heterocychc and carbo-cychc compounds. The esters, ketones and aldehydes are more stable when the reaction takes place on solid supports than in the hquid-phase, because this immo-bihzed components are not so sensitive towards water or oxygen. In the total synthesis of (S)-zearalenone (155) on solid supports the Grignard reaction is one of the key steps (Scheme 3.16) [120]. 

In their papers Rodionov and coworkers described the polymerization of organolithium compounds in terms of the formation of lithium bonds (Scheme 1), analogous to hydrogen bonds, which brought about cyclic or linear association of these compounds in solution . However, the strong association of alkyllithium compounds, persisting even in the vapour phase, indicates that their association takes place through the formation of... 

The complex formation between ethyl and t-butyllithium in benzene was later investigated by Weiner and West by spectroscopic methods. The new organolithium compounds differ from any pure component, but contain both types of alkyl groups bonded to lithium. 

---