Reductive Lithiation using Lithium Metal

Preparation of Organoiithium Compounds from Another Organoiithium Compounds 

DG directing group based on helerostom substitution chart 1.2 Reactivity in deprotonation 

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A number of substituted cyelopropanes have been prepared by reductive lithiation of various l,l-bis(phenylsulfanyl)cyclopropanes followed by reactions of the resulting a-phenylsulfanyl-cyclopropyl anions with selected electrophiles. Metalation can be carried out by several methods, cf 1, ° but reduction with two equivalents of lithium naphthalenide in tetrahyd-rofuran at — 70°C is the most efficient. The product yields are generally satisfactory with carbon dioxide and benzaldehyde as trapping agents. Thus, when 2-methyl-1,1-bis(phenylsul-fanyl)cyclopropane was used as starting material, 2-methyl-l -(phenylsulfanyl)cyclopropanecar-boxylic acid (2 b) and (2-methyl-l-phenylsulfanylcyclopropyl)(phenyl)methanol (3 c) were obtained in 86 and 76% yield, respectively. ... 

Various effective synthetic routes can be based on metallation of organic substrates with lithium arenes, obtained in situ from metallic lithium and an arene present in substoichio-metric amounts. Immediate quenching of the lithiated intermediates may be considered as a reduction reaction of the original substrate. Otherwise, further functionalization may be attained when using diverse electrophiles. Various examples of such processes follow (see also equation 69 in section VI.B.l). 

Since different reactivity is observed for both the stoichiometric and the catalytic version of the arene-promoted lithiation, different species should be involved in the electron-transfer process from the metal to the organic substrate. It has been well-established that in the case of the stoichiometric version an arene-radical anion [lithium naph-thalenide (LiCioHg) or lithium di-ferf-butylbiphenylide (LiDTBB) for using naphthalene or 4,4 -di-ferf-butylbiphenyl (DTBB) as arenes, respectively] is responsible for the reduction of the substrate, for instance for the transformation of an alkyl halide into an alkyllithium . For the catalytic process, using naphthalene as the arene, an arene-dianion 2 has been proposed which is formed by overreduction of the corresponding radical-anion 1 (Scheme 1). Actually, the dianionic species 2 has been prepared by a completely different approach, namely by double deprotonation of 1,4-dihydronaphthalene, and its X-ray structure determined as its complex with two molecules of N,N,N N tetramethylethylenediamine (TMEDA). ... 

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