Reaction mechanisms organolithium compounds

The mechanism of the reaction between a hydrocarbon organolithium compound and a carbonyl compound is well-documented [69] and has been suggested earlier for fluorine-containing compounds [32, 68, 70] More recent studies on the mechanism have resulted m a better understanding ol this reaction [71] (equation 37)... 

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. 

The same reaction mechanism—again corresponding to strategy 1 of Figure 6.41— explains why carboxylic acids and two equivalents of an organolithium compound react selectively to form ketones (Figure 6.45, substrate on the left). The first equivalent of the reagent... 

The reaction of Grignard reagents and organolithium compounds with aldehydes and ketones is perhaps the most useful method for the preparation of alcohols. The reaction is conducted under basic conditions and proceeds according to the following general mechanism ... 

Another type of reaction relying on the same fundamental mechanism involves organolithium compounds <85JA4700>. The general scheme is depicted in Equation (29). The vinyl carbanion product isomerizes rapidly even at — 70 °C, hence a mixture of ( ) and (Z) isomers is obtained upon reaction with electrophiles. This kind of chemistry has been used to prepare some unusual phos-phino-l,2,3-butatrienes (Equation (30)) <92SL635>. Formally involving an hydride ion and related to the same scheme is the reaction of a phosphirene imine with a borane complex (Equation (31)) <94CB313>. 

This striking effect of a strong donor base on the catalytic activity of an organolithium compound contrasts with the reverse effect of donor bases on the growth reaction of ethylene with trialkylaluminum compounds. The catalytic activity of the latter is connected with the electron deficient nature of the uncoordinated, monomeric, trialkylaluminum species (10). These facts point to a difference in the mechanism of ethylene addition between the amine-coordinated organolithium catalyst and the trialkylaluminum compounds. 

Few detailed mechanistic studies of reactions of organolithium reagents are known, apparently because of the high specific rate constants exhibited by most of these processes, coupled with the sensitivity of these organometallic compounds toward oxygen and water. Nevertheless the last several years have afforded much data which indicate the direction that research in reaction mechanisms in this area, as well as in others, is taking or should take. Specifically, they first involve the problems of structure and the effect of solvent on structure 1-14). This area has been reviewed by Brown (i). 

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