Compounds lithiated

Dibenzofurans behave like 0,0-disubstituted diphenyl ethers, i.e. they undergo substitution reactions typical for benzenoid compounds. Halogenation, sulfonation and acylation occur in the 2-position, and subsequently 2,8-disubstituted compounds are formed. Nitration yields 3-nitro- and then 3,8-dinitro compounds. Lithiation and mercuration lead to 4-substituted and finally to 4,6-disubstituted products [13]. 

Compounds lithiated state Compounds delithiated state Redox potential (V) Capacity (mAh g ) References... 

The reaction of lithiated cumulenic ethers with ethylene oxide, trimethyl-chlorosilane and carbonyl compounds shows the same regiosnecificity as does the alkylation. 

The Li compound 588 formed by the ort/io-lithiation of A. A -dimethylaniline reacts with vinyl bromide to give the styrene derivative 589(433]. The 2-phe-nylindole 591 is formed by the coupling of l-methyl-2-indolylmagnesium formed in situ from the indolyllithium 590 and MgBr2, with iodobenzene using dppb[434]. 2-Furyl- and 2-thienyllithium in the presence of MgBr2 react with alkenyl halides[435]. The arylallenes 592 and 1,2,4-alkatrienes are prepared by the coupling reaction of the allenyllithium with aryl or alkenyl halides[436]. 

The second step is also heterogeneous and involves the breakdown of the intermediate compound with further lithiation into lithium sulfide [12136-58-2] and finely divided iron [7439-89-6] particles. 

Competitive metallation experiments with IV-methylpyrrole and thiophene and with IV-methylindole and benzo[6]thiophene indicate that the sulfur-containing heterocycles react more rapidly with H-butyllithium in ether. The comparative reactivity of thiophene and furan with butyllithium depends on the metallation conditions. In hexane, furan reacts more rapidly than thiophene but in ether, in the presence of tetramethylethylenediamine (TMEDA), the order of reactivity is reversed (77JCS(P1)887). Competitive metallation experiments have established that dibenzofuran is more easily lithiated than dibenzothiophene, which in turn is more easily lithiated than A-ethylcarbazole. These compounds lose the proton bound to carbon 4 in dibenzofuran and dibenzothiophene and the equivalent proton (bound to carbon 1) in the carbazole (64JOM(2)304). 

Neutral azoles are readily C-lithiated by K-butyllithium provided they do not contain a free NH group (Table 6). Derivatives with two heteroatoms in the 1,3-orientation undergo lithiation preferentially at the 2-position other compounds are lithiated at the 5-position. Attempted metallation of isoxazoles usually causes ring opening via proton loss at the 3-or 5-position (Section 4.02.2.1.7.5) however, if both of these positions are substituted, normal lithiation occurs at the 4-position (Scheme 21). 

Most isothiazoles are lithiated at the 5-position by the action of butyllithium or other organolithium compounds, provided that this position is vacant (65AHC(4)107, 72AHC(14)l, 77SST(4)339). 3-Methyl-4-nitroisothiazole, however, is inert (65AHC(4)107). 2,1-... 

Isothiazole itself is best prepared by the reaction between propynal, ammonia and sodium thiosulfate (see Section 4.17.9.3). A wide range of substituted mononuclear isothiazoles can be obtained by oxidative cyclization of y-iminothiols and related compounds (see Section 4.17.9.1.1). Substituents at the 3-position need to be in place before cyclization, but 4-substituents are readily introduced by electrophilic reagents (see Section 4.17.6.3), and 5-substituents via lithiation (see Section 4.17.6.4). 

This procedure illustrates a general method for the preparation of alkenes from the pal 1 adium(Q)-cata1yzed reaction of vinyl halides with organo-lithium compounds, which can be prepared by various methods, including direct regioselective lithiation of hydrocarbons. The method is simple and has been used to prepare a variety of alkenes stereoselectively. Similar stoichiometric organocopper reactions sometimes proceed in a nonstereoselective... 

The methodology of heteroatom-directed lithiation has been applied to the synthesis of a variety of organochalcogen compounds, including unstable, low-valent compounds (Section 15.6). ° The Se N interactions in the diselenide 15.4 activate the Se-Se bond toward insertion of a sulfur atom or a methylene group to give the derivatives 15.21a,... 

RR C=NLi) . They can be prepared in high yield either by the addition of an organolithium compound across the triple bond of a nitrile (equation (1)) or by lithiation of a ketimine (equation (2)). 

Reaction of lithiated allene with methoxymethyl isothiocyanate afforded 107, after trapping with methyl iodide. The newly formed 107 isomerizes under mild conditions to triene 108. This compound is ideally setup to experience an electrocyclization to dihydropyridine 109. Heating in the presence of acid facilitates aromatization of 109 to pyridines 110. 

Halogeno compounds have been prepared by direct halogena-tion or by Sandmeyer reaction on 4-aminoisothiazoles. As expected from general considerations, a halogen atom in the 4-position is less reactive than one in the 5-position, but nitriles are obtained in good yield with cuprous cyanide at elevated temperatures. With butyllithium, lithiation occurs exclusively in the 5-position, and no evidence of halogen displacement has been obtained. ... 

The ease with which furans may be formed from and hydrolyzed back to 1,4-dicarbonyl compounds, together with ready 5-lithiation of 2-substituted furans. 

---