Lithium metal, reductive lithiation with

When there is no programmed radical cyclization reaction as discussed in the preceding section, the anomeric radical generated under reductive metallation conditions will obviously be reduced to an organometallic. This is no longer radical chemistry but the radical initiation will impose the stereoselectivity of the anionic process that follows if kinetic conditions are maintained. This situation is observed in the reductive lithiation with lithium naphthalenide (LN) of derivatives 10 where X can be Cl, SPh, or SOjPh (Fig. 13), a process first reported on cyclic a-alkoxyphenyl sulfides. ... 

Because of the similar potentials between fully lithiated graphite and lithium metal, it has been suggested that the chemical nature of the SEIs in both cases should be similar. On the other hand, it has also been realized that for carbonaceous anodes this formation process is not expected to start until the potential of this anode is cathodically polarized (the discharge process in Figure 11) to a certain level, because the intrinsic potentials of such anode materials are much higher than the reduction potential for most of the solvents and salts. Indeed, this potential polarization process causes one of the most fundamental differences between the SEI on lithium metal and that on a carbonaceous anode. For lithium metal, the SEI forms instantaneously upon its contact with electrolytes, and the reduction of electrolyte components should be indiscriminate to all species possible,while, on a carbonaceous anode, the formation of the SEI should be stepwise and preferential reduction of certain electrolyte components is possible. 

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. ... 

Simple, unfunctionalized organolithium compounds are usually prepared by reductive lithiation of alkyl halides with lithium metal at ambient temperature or above [26]. Reductive lithiation is fastest for alkyllithium compounds (the more substituted the better) and slowest for aryllithium compounds. The order of reactivity follows logically from the relative stabilities of the intermediate radicals, whose formation is the rate-determining step of the sequence. 

Various functionalized organocopper species have been prepared starting from organolithiums[lcj. Thus, PhMe2SiLi, which is readily prepared by the reductive lithiation of PhMejSiCl with lithium metal, is readily converted to the correspond-... 

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). ... 

Polymetalated systems of this type without phenyl substitution at the lithiated carbon centre are only accessible when solutions of LiCioHg (144a) or LiDBB (145) in THF instead of a suspension of metallic lithium in THF are reacted with bis(phenylthiomethyl)silanes of type 155. In our group, variously substituted bis(lithiomethyl)silanes 117a, 156b-e and 101 were synthesized by reductive cleavage of the carbon-sulphur bond with LiCioHg... 

In contrast to these experimental and computational results, lithiated 1-silafluorenide 50, which was prepared by the reductive cleavage of the central Si—Si bond of disilane 49 with lithium under ultrasonic activation, provides some evidence for the existence of localized metalated siloles (equation 55)111. Thus, upon metalation of 49 to form 50, a highfield shift of the 29Si nucleus (AS = —47.9 ppm) is observed. In addition, the chemical shifts of the phenyl carbons indicate that there is no accumulation of tt electron density, which would be expected for a delocalized lithium silafluorenide111. 

Intermediates 663 can be prepared by tin-lithium transmetallation with w-BuLi from a-stannylated vinyl sulfides974. Starting from l,l-bis(arylsulfanyl)ethenes, a reductive metallation with lithium naphthalenide at —70°C is a very efficient approach to lithiated vinyl sulfides975,976. Other methods involved bromine-lithium exchange977 or addition of methyl or phenyllithium to thioketenes978. A convenient method for the preparation of l-(methylsulfanyl) and l-(phenylsulfanyl) vinyllithiums was the treatment of 2-methoxyethyl sulfides with 2 equiv of w-BuLi-TMEDA at — 30 °C979. 

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