Hydrogenation organolithiums

Reaction of various reagents (CH3I. CjHjI, PhCHO) on the organolithium products obtained by reaction of butyl-lithium with 2-methyl-4-phenylthiazole gives approximately 90% 5-substitution. The increased reactivity of the hydrogen in the 5-position can be explained by the fact that the -r J effect of a 4-methyl group would increase the electron... 

In earlier studies [f J], it was shown that pentafluorobenzene has an acidic aryl hydrogen capable of metalation by organolithium or organomagnesium compounds to yield perfluorophenylorganometallic compounds... 

With a difluoroethylene containing hydrogen and chlonne, where both groups can be replaced by lithium, a mixture of two organolithium compounds is formed in a 2 1 ratio, indicating a more facile replacement of chlorine [63] (equation 30)... 

The reaction of tnfluoromethyl-substituted A -acyl umnes toward nucleophiles in many aspects parallels that of the parent polyfluoro ketones Heteronucleophiles and carbon nucleophiles, such as enarmnes [37, 38], enol ethers [38, 39, 40], hydrogen cyanide [34], tnmethylsilylcarbomlnle [2,47], alkynes [42], electron-nch heterocycles [43], 1,3-dicarbonyl compounds [44], organolithium compounds [45, 46, 47, 48], and Gngnard compounds [49,50], readily undergo hydroxyalkylation with hexafluoroace-tone and amidoalkylation with acyl imines denved from hexafluoroacetone... 

Metalation of Thiophenes with Organolithium Compounds (Nucleophilic Substitution on Hydrogen)... 

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. 

A more recent application of this chemistry was reported by Oestreich and Hoppe [74] and involved the enantioselective deprotonation of the enyne carbamate ester 125 with sec-butyllithium in the presence of (-)-sparteine (Scheme 2.41). Removal of the pro-S hydrogen atom led to the corresponding organolithium intermediate, which then underwent a highly enantioselective intramolecular 1,4-addition to the enyne. Protonation of the resulting allenyllithium species 126 provided a 70 30 mixture of the two diastereomeric allenes 127. 

Halogen-lithium exchange of iodide 71 and subsequent addition of 2-acetyl-furan (72) to the resultant organolithium intermediate yielded two diastereomeric tertiary alcohols (dr=l l), which were converted to (E)-olefin 73 with complete diastereoselectivity upon brief exposure to catalytic amounts of concentrated aqueous hydrogen chloride (Scheme 11) [18]. Diastereoselective hydroboration/oxidation of 73 gave largely the desired stereoisomer 74 due to... 

The only measured enthalpy of vaporization is for n-butyl lithium, 107.1 2.9 kJmoU, from which the constant b(Li) in equation 4 is derived as 85 kJmoU. This is a hefty value compared to fc(OH) = 29, b(—S(0)2—) = 53 and b(CY) = 11 kJmoU. However, the oligomeric states of the organolithium liquid and gas phases are not known with certainty. This is reminiscent of problems for hydrogen-bonded species such as carboxylic acids and hydrogen fluoride. 

In their papers Rodionov and coworkers described the polymerization of organolithium compounds in terms of the formation of lithium bonds (Scheme 1), analogous to hydrogen bonds, which brought about cyclic or linear association of these compounds in solution . However, the strong association of alkyllithium compounds, persisting even in the vapour phase, indicates that their association takes place through the formation of... 

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