Group dilithium

If one of the groups R is Ph or SR, the abstraction of the second proton is much faster. Allenes give the same dilithium compounds as their acetylenic isomers . 

A characteristic reaction of sulfmylimines RNSO is the quantitative addition of R Li reagents to form adducts of the type Li[RNS(R )NR]. ° The structures of these sulfmimidinates are discussed in Section 10.4.4." The reactions of RNSO derivatives with two equivalents of lithium tert-butylamide result in the formation of diazasulfite anions [OSNR(N Bu)] (9.12) (Eq. 9.12)." The dilithium derivatives of these dianions form hexameric thirty-six atom (Lii2Ni206S6) clusters with structures that are dependent on the nature of the R group. 

The dilithium phosphandiide dimer 9 is complexed by two molecules of a fluorosilane. The complex crystallizes in the monoclinic space group P2i/n. The framework of the aggregate consists of a cen-... 

The proposed mechanism of this reaction is based on the nucleophilic attack of the alkyllithium compound at the carbenoid carbon atom or at the a-lithiooxy carbene. The dilithium compound 102 gives the alkene 103 by the loss of lithium oxide (equation 56). When an alkoxy residue, which is a better leaving group than U2O, is offered in the a-position of the corresponding dilithium compound, the elimination of lithium alkoxide takes place instead of lithium oxide. This is illustrated by the reaction of epoxide 104 that delivers the allylic alcohol 105 upon treatment with n-butyllithium (equation The... 

The related geminal dilithiated compound 11 was generated by the same group by reaction of a substituted sulphoximine with 2.5 equivalents of n-butyllithium in THF (Figure 4) Also in this case, the crystal structure of the dilithium compound could be cleared up by X-ray structural analysis (Figure 5). 

In the group of Izod, the tris(phosphane oxide) 19 was 1,2-dilithiated by the reaction with two equivalents of w-butyllithium in THF at room temperature (Scheme 7). The similarity of the structural formula of compound 20 (Lewis formula) to 1,2-dilithium compounds found by Sekiguchi and coworkers (see Section n. E), where two lithium centres are bridging a C2 unit, is not maintained in the solid state. The X-ray structural analysis reveals a centrosymmetric dimer containing no carbon-lithium contacts (Figure 8). 

By cobalt-lithium exchange, the group of Sekiguchi and coworkers generated several dilithium salts of variously substituted cyclobutadiene dianions . By the reaction of the functionalized acetylenes (e.g. compound 137) with CpCo(CO)2 (136), the corresponding cobalt sandwich complexes, related to compound 138, were obtained (Scheme 50). These can be interconverted into the dilithium salts of the accordant cyclobutadiene dianions (e.g. dilithium compound 139) by reaction with metallic lithium in THF. Bicyclic as well as tricyclic (e.g. dilithium compound 141, starting from cobalt complex 140) silyl substituted systems were generated (Scheme 51) . ... 

The solution structure of the dilithium compound 237, generated by treating frawi-1,2-diphenyl-l,2-bis(trimethylsilyl)ethylene (236) with excess lithium metal in THF (Scheme 83), was studied by ID and 2D NMR techniques in the group of FUrstner". As a conclusion, the dilithium compound 237 adopts a C2-symmetric twisted frawi-arrangement with two bridging lithium centres in solution, underlining the various X-ray structural studies in the solid state by Sekiguchi and coworkers. 

The reduction of l,l-bis(diphenylphosphanyl) ethylene (248) with an excess of metallic lithium, activated by ultrasonic irradiation, leads to C—C coupling under the formation of a l,l,4,4-tetrakis(diphenylphosphanyl)butane (249) (Scheme 88)". Surprisingly, the lithium centres in the resulting dilithium compound do not form any lithium-carbon contacts, being coordinated by two diphenylphosphanyl groups and two TFIF molecules each. With this strucmral motif, the molecular structure is similar to the one of tris(phosphaneoxide) 20 (Section n. A), also obtained by Izod and coworkers upon deprotonation. ... 

Examples of this approach to the synthesis of ketones and carboxylic acids are presented in Scheme 1.6. In these procedures, an ester group is removed by hydrolysis and decarboxylation after the alkylation step. The malonate and acetoacetate carbanions are the synthetic equivalents of the simpler carbanions lacking the ester substituents. In the preparation of 2-heptanone (entries 1, Schemes 1.5 and 1.6), for example, ethyl acetoacetate functions as the synthetic equivalent of acetone. It is also possible to use the dilithium derivative of acetoacetic acid as the synthetic equivalent of acetone enolate.29 In this case, the hydrolysis step is unnecessary, and decarboxylation can be done directly on the alkylation product. 

Another type of adducts [8, Eq. (3)] was formed by the reaction of di(fert-butyl)aluminum chloride with dilithium bis(trimethylsilyl)hydrazide in low yields below 30% [19]. The structure of 8 consists of a distorted heterocubane with four vertices occupied by nitrogen atoms, two of which are connected by an intact N—N bond across one face of the cube. The cation positions are occupied by two aluminum and two lithium atoms, of which the last ones bridge the N—bond. Part of the hydrazide molecules was cleaved, and the aluminum atoms are bonded to one ferf-butyl group only. On the basis of the NMR spectroscopic characterization many unknown by-products were formed in the course of that reaction, and no information is available concerning the reaction mechanism. Compound 8 may be described as an adduct of dilithium bis(trimethylsilyl)hydrazide to a dimeric iminoalane containing a four-membered AI2N2 heterocycle. Further... 

Alkylation of isoprene at the methyl group was achieved through the reaction of the corresponding metal derivative (fert-BuOK-lithium tetramethylpiperidine, THF) with 1-bromoheptane (60% yield).257 Regioselective monoalkylation of isoprope-nylacetylene can be performed in high yields through the dilithium derivative 258... 

The presence of an NH group is essential, since the Boc-p-amino sulfone derived from Pro could only be coupled with lower yields (-20%). This method is also suitable for the preparation of pseudodipeptides having functionalized side chains such as those of Ser and AsnJ72l The p-oxo sulfone 51, which was obtained by reacting Boc-pAla-OMe with the dilithium anion of methyl phenyl sulfone, cleanly reacted with ethyl bromoacetate to give the p-oxo sulfone 52 (86%). The latter was reduced using LLAIH4, which on reductive elimination produced the over-reduced Boc-Alai)i(CH2—CH2]Gly-OMe isostere (80%). 

The anionic complexes (50) are obtained from the group VI carbonyl and the dilithium derivatives of the hydroxyalkynes HC=CCR2(OH) subsequent protonation or acylation affords propadienylidene (51) or carbene (52) complexes by complex cyclization and addition reactions (Scheme 3) (28). Attempts to obtain the dimethyl complex by reaction of the chromium alkynolate dianion with COCl2 gave only polymeric material. More stable complexes were obtained with R = aryl (73). 

The Zr-based route to main group heteroles is a convenient alternative to the method using l,4-dilithio-2,3-butadienes (see Section II.B.l.a), the more so as these dilithium reagents are easily available from zirconacyclopentadienes. Thus, the synthesis of 1,1-dichloro-2,3,4,5-tetramethylsilole (27) was readily performed from 70 by use of the I2In-BuLi/SiCLt sequence of reagents40 (see Section II.B.l, equation 8)... 

Silicon-bridged [l,l]metallocenophanes of type 40 in Scheme 14 represent another class of dinuclear compounds with the ligand system (30). The synthesis of the 1,1,12,12-tetramethyl [1,1] silaferrocenophane was reported by two groups only recently. In one procedure, the dilithium salt of dicyclopentadienyldimethylsilane was reacted with ferrous chloride to give a mixture of the metallocenophane with poly(ferrocenyldimethylsilane) (equation 55)124. In the other procedure, this compound was prepared in a multistep synthesis starting from dilithio ferrocene, as shown in equation 56125... 

Hindered cuprates. A novel route to lithium dialkylcuprates containing a secondary or a tertiary alkyl group involves reaction of the tosylhydrazone of an aldehyde with a copper reagent, such as dilithium trimethylcuprate (6, 386 7, 115). An example is shown in equation (I) for preparation of a cuprate containing the t-butyl group.1... 

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