Carbon atoms phenyllithium

The crystal structures of many organolithium compounds have been determined.44 Phenyllithium has been crystallized as an ether solvate. The structure is tetrameric with lithium and carbon atoms at alternating corners of a highly distorted cube. The lithium atoms form a tetrahedron and the carbons are associated with the faces of the tetrahedron. Each carbon is 2.33 A from the three neighboring lithium atoms and an ether molecule is coordinated to each lithium atom. Figures 7.2a and b show, respectively, the Li-C cluster and the complete array of atoms, except for hydrogen 45 Section 6.2 of Part A provides additional information on the structure of organolithium compounds. 

Similar conclusions are reached for the distribution of electron density in the isomeric adduct 101, where the carbon atoms adjacent to the reaction center are shifted upheld with respect to the corresponding 1,4-dihydropyridazine. Somewhat higher shielding is found for the C-5 atom (8.0 ppm) than for C-3 (3.7 ppm), but in either position the electron density appears to be appreciably lower than for C-4 in adduct 100. Such differences are presumably to be related to the nature of the lithium-nitrogen bond, but clearly to a hrst approximation all the adducts from diazines and phenyllithium can be described as undissociated species, whether that bond is ionized or strongly polar covalent. 

In the steroid field, Z eric and Chavez-Limon1 05 have produced 5a-hy droxy--phenyl derivatives by adding phenyllithium to 6 ,6a-epoxy steroids Eq. 806). Attack of the reagent at Cw of the Bteroid skeleton is consistent with the fact that this is the less-alkylated terminal epoxide carbon atom i.e. the loast hindered), and also with the fact that a diaxi l product is thereby obtained. 

The carbonyl carbon atom in the octahydro-l-pyrindones undergoes typical carbonyl addition reactions.142-147 For example, the cyanohydrin (213) is obtained from the corresponding oxo compound. Alcoholysis of 213 gives the ester.142 Phenyllithium adds smoothly to I,2-dimethyI-4-oxo-perhydro-l-pyrindine (207) to give 214.143-145... 

The anions of Reissert compounds 19 and 20 undergo reaction with aldehydes to form esters of secondary alcohols containing the 2-quinolyl or 1-isoquinolyl group bonded to the carbinol carbon atom. Thus benzaldehyde, l-benzoyl-l,2-dihydroquinaldonitrile (7), and phenyllithium in ether-dioxan at — 10° gave 29, and benzaldehyde, 2-benzoyl-l,2-dihydroisoquinaldonitrile (8), and phenyllithium in ether-dioxan at —10° (or sodium hydride in refluxing... 

The sole method of synthesis that has been developed thus far involves the formation of a diGrignard or dilithio reagent from o,o -dibromobi-benzyl. The dibromo derivative is prepared by the coupling of o-bromobenzylbromide with phenyllithium (215). An alternative route that would utilize ring closure at the bridging carbon atoms (i.e., a site remote from the heteroatom) has not yet been explored. The dibenzazepin and dibenzoxepin derivatives have been prepared by this approach 35). The Grignard reactions are summarized in Eq. (97). 

Carbonyl compounds are capable of undergoing another completely different sort of reaction, in which the carbonyl oxygen is replaced, not by a heteroatom as we saw above, but by an sp carbon atom. When triphenylphosphine is treated with a secondary aliphatic halide, a normal substitution reaction occurs, resulting in the replacement of the halide by the phosphorus compound. This phosphonium salt adduct may then be treated with a very strong base, such as phenyllithium, to produce an ylid. An ylid is a compound in which there is a positive charge adjacent to a negative charge. Write down this reaction sequence. 

Methanolysis of (108a) furnishes the thioxosulfonamide (145) as yellow crystals in quantitative yield (Scheme 53) <78AG(E)195>. n-Butyllithium and phenyllithium are commonly used as nucleophiles and attack the sulfur atom, but the lithium salts of isocyanides attack mainly the carbon atoms of the ring. Attack on the sulfur atom of the thiiranimine (108c) is observed in the reactions with the anion of diethyl malonate, a phosphorus ylide, /V-methylindole and enamines or ynamines (Scheme 54) <80JOC4366>. 

Alkylation a to a cyclopropane ring has also been achieved using activation by the triphenyl-phosphonio and diphenylphosphoryl groups and an aromatic function attached to a carbon atom a to the ring. Reaction of these compounds with a strong base (lithium diisopropylamide or phenyllithium) resulted in anion formation, the anions were treated with benzophenone, iodomethane, and methyl chloroformate, e.g. reaction of 5 with aceto-phenone. ... 

A Phenyllithium is polarized such that the phenyl group is car-banionic in character and behaves as a strong base, abstracting the 2-H of fluorobenzene. The resulting ortho lithiation is followed by loss of lithium fluoride to form the benzyne intermediate. The second molecule of phenyllithium adds across the triple bond in a non-selective manner to generate biphenyl with 50% of the product with the aryl-aryl bond at the original labelled carbon atom, according to the mechanism in Scheme 9.8. 

According to Wittig,97 the base (sodium alkoxide, phenyllithium, or sod-amide) removes a proton from the -carbon atom, yielding the unstable ylide in which the benzyl group then migrates from nitrogen to carbon. 

Subtle structural differences have been observed in some dimers of lithiated 1,3-bis[(dimethylamino)alkyl]benzenes [14]. Direct lithiation of l,3-bis[(dimethylami-no)ethyl]henzens with H-butyllithium produced a symmetric dimer, in which the coordination sphere of lithium was saturated by coordination of the chelating amino substituents. An analogous lithiation reaction performed between 1,3-bis[(dimethylamino)/ ro 7y/]benzene and n-butyllithium yielded a mixed dimeric aggregate comprising the expected phenyllithium derivative and nBuLi in a 1 1 molar ratio. In the molecular structure four lithium ions and four bridging carbon atoms form a ladder-type framework. 

The acidity of a hydrogen atom bound to a carbon atom increases when the % of atomic p orbital decreases in the hybridization of this carbon acetylene sp C) is thus much more acidic pKa = 24) than benzene sp C, pK = 37), itself more acidic than butane sp C, pA = 44). The acido-basic equilibrium between butyl lithium and acetylene (or benzene) is displaced towards the direction that is favorable for the reaction producing lithium acetylide (or phenyllithium) and butane (or benzene). 

When the organohthium reagent is inexpensive, as in the case of phenyllithium, it is customary to add two equivalents of the reagent direcdy to the carboxylic acid. The first equivalent reacts with the carboxylic acid to form the lithium carboxylate salt. The second equivalent reacts with the carbonyl carbon atom of the carboxylate ion. 

In this context, one may also pay attention to the so-called "betaine-ylides" that act as key intermediates in stereocontrolled Wittig olefination reactions. They are generated from the ordinary adducts obtained by the combination of a phosphine ylide and an aldehyde in the presence of lithium bromide (or another soluble lithium salt). When the P-betaines are a-deprotonated with phenyllithium, the stereocenter at the phosphorus-adjacent carbon atom becomes configurationally mobile. In this way, erythro/threo mixtures can spontaneously convert into virtually pure /Areo-betaine ylides (p-lithiooxy ylides, P-oxido ylides). Reprotonation and subsequent elimination of triphenylphosphine oxide affords trans olefins, whereas a-substitution by electrophiles other than acids leads to branched alkenes exhibiting a well-defined stereochemistry "("three-dimensional"" Wittig reaction or SCOOPY method). ... 

Favoring a "thiophilic reaction mode," phenyllithium binds directiy to the sulfur atom of thiobenzophenone to give diphenyl(phenylthio)methyllithium (90 Scheme l-62). A preceding nucleophilic addition onto the unsaturated carbon atom ("carbophilic mode") followed by phenyl migration can be ruled out in the given case although it was demonstrated to happen with thiobenzophenone, thiocamphor, and vinylmagnesium bromide. 

The addition of n-butyllthium, phenyllithium or another organolithium on the central carbon atom of dicyclohexylcarbodiimide furnishes a 1,3-diazaallyl species. Upon neutralization, an amidine (iminoamide) is obtained. - ... 

The compounds with three ligands should have the T-shaped stereochemistry characteristic of 10-electron species on VSEPR theory. For three carbon ligands, triphenyliodine, prepared from diphenyliodine(III) iodide and phenyllithium at -80 °C in ether,61 decomposes at —10 °C, and even more stable compounds, with cyclic structures involving the iodine atom,62 still decompose over relatively short periods. No crystal structures have been determined, although NMR studies support the structural assignment.62... 

Transition metal compounds with covalent carbon-metal bonds include organo-zinc, organo-cadmium, and organo-mercury compounds. Carbon-13 shifts of the methyl derivatives (Table 4.71) indicate a heavy atom deshielding. Diphenylmercury displays carbon shifts similar to those of phenyllithium and phenylmagnesium bromide (Table 4.53). 

Thus, in alkylphosphonium salts too the C—H functions adjacent to the positively charged key atom were too acidic to let the attacking nucleophile proceed on its way towards the phosphorus center. A way out of this dilemma should consist in the application of a phosphonium salt with less acidic neighboring C—H functions. Such a salt was tetraphenylphosphonium iodide which in the reaction with phenyllithium did indeed lead to the first compound containing five covalent carbon-element bonds, pentaphenylphosphorane, (C6H5)5P (12)23). Its covalent nature was... 

The ylide is prepared by deprotonating a triphenylalkylphosphonium salt with a strong base, commonly an organometallic base such as butyllithium or phenyllithium. The hydrogens on the carbon that is bonded to the phosphorus of the salt are somewhat acidic because the carbanion of the conjugate base (the ylide) is stabilized by the inductive effect of the positive phosphorus atom. In addition, a resonance structure with five bonds to phosphorus makes a minor contribution to the structure and provides some additional stabilization. The triphenylalkylphosphonium salt can be prepared by an SN2 reaction of triphenylphosphine with the appropriate alkyl halide (see Section 10.9). 

The oxygen atom of acyl metallates may present nucleophilic character (Figures 3.25, 4.16). In 1964, E. O. Fischer showed that protonation of the benzoyl tungstate complex obtained from W(CO)6 and phenyllithium (Figure 3.20) provided the first characterized example of a metal-carbon double bond, viz. the hydroxycarbene complex (CO)5W=C(OH)Ph. This labile species decomposed to provide ben-zaldehyde however, it could be esterified with diazomethane to provide... 

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