Organo lithium metal

All that has been said in this section applies with equal force to the use of organo-lithium reagents in the synthesis of alcohols. Grignard reagents are one source of nucleophilic carbon organolithium reagents are another. Both have substantial carbanionic char acter in their- car bon-metal bonds and undergo the same kind of reaction with aldehydes and ketones. 

The rearrangement of an ether 1 when treated with a strong base, e.g. an organo-lithium compound RLi, to give an alcohol 3 via the intermediate a-metallated ether 2, is called the Wittig rearrangement. The product obtained is a secondary or tertiary alcohol. R R can be alkyl, aryl and vinyl. Especially suitable substrates are ethers where the intermediate carbanion can be stabilized by one of the substituents R R e.g. benzyl or allyl ethers. 

Organocadmium compounds can be prepared from Grignard reagents or organo-lithium compounds by reaction with Cd(II) salts.180 They can also be prepared directly from alkyl, benzyl, and aryl halides by reaction with highly reactive cadmium metal generated by reduction of Cd(II) salts.181... 

Several examples of intramolecular additions to carbonyl groups by organo-lithium reagents generated by halogen-metal exchange have been reported, such as the two examples shown below. What relative reactivity relationships must hold in order for such procedures to succeed ... 

In many syntheses activation is not effected by sonochemical preparation of the metal alone but rather by sonication of a mixture of the metal and an organic reagent(s). The first example was published many years ago by Renaud, who reported the beneficial role of sonication in the preparation of organo-lithium, magnesium, and mercury compounds [86]. For many years, these important findings were not followed up but nowadays this approach is very common in sonochemistry. In another early example an ultrasonic probe (25 kHz) was used to accelerate the preparation of radical anions [87]. Unusually for this synthesis of benzoquinoline sodium species (5) the metal was used in the form of a cube attached to the horn and preparation times in diethyl ether were reduced from 48 h (reflux using sodium wire) to 45 min using ultrasound. 

The most widely used method for the preparation of organometallic compounds of the heavier alkali metals is from the corresponding organo-lithium reagent and an alkoxide. 

Metallic lithium in the form of a suspension has been used to polymerize isoprene (97) but the system is not too suitable for an exact analysis of the mechanism. The conversion-time curves are sigmoidal in shape. Minoux (66) has shown that the overall rate is not very dependent on the amount of lithium dispersion used as expected if the organo-lithium intermediates are highly associated. The molecular weight of the polymer is more dependent on quantity of lithium used. The observed kinetic behaviour is very similar to that shown in lithium alkyl initiation. This suggests that apart from differences in the initiation step, the mechanisms are quite similar. 

Snyder703 was the first to obtain an organo-lithium derivative of pyrazole, when he treated l-phenyl-3-methylpyrazole with butyl-lithium and then carbon dioxide, and isolated l-phenyl-3-methyl-pyrazole-5-carboxylic acid. Subsequently, Alley704 showed that 1-phenyl- and 1-methyl-pyrazoles are also metallated in the 5-position by the treatment with organo-lithium compounds. Hiittell and Schon705 studied the pyrazolyl lithium derivatives in detail, and showed that in pyrazole itself the 3- and 5-hydrogen atoms were more... 

The related f-butyl derivative 347 was metallated with w-BuLi and the resulting organo-lithium compound 348 was alkylated with alkyl and allyl iodides, bromides and chlorides in the presence of HMPA519. From 349, several different types of deprotection reactions were possible. Direct hydrolysis to the corresponding aldehydes has been performed under... 

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