N-Butyllithium-TMEDA

Methylthiophene is metallated in the 5-position whereas 3-methoxy-, 3-methylthio-, 3-carboxy- and 3-bromo-thiophenes are metallated in the 2-position (80TL5051). Lithiation of tricarbonyl(i7 -N-protected indole)chromium complexes occurs initially at C-2. If this position is trimethylsilylated, subsequent lithiation is at C-7 with minor amounts at C-4 (81CC1260). Tricarbonyl(Tj -l-triisopropylsilylindole)chromium(0) is selectively lithiated at C-4 by n-butyllithium-TMEDA. This offers an attractive intermediate for the preparation of 4-substituted indoles by reaction with electrophiles and deprotection by irradiation (82CC467). 

Polymerization of I. I was polymerized in flame-dried equipment under N 2 at -40 °C as follows. A 25-mL round-bottom flask equipped with a poly(tetra-fluoroethylene) (Teflon)-covered magnetic stirring bar and rubber septum was charged with I (1.2 g, 10.9 mmol) (5, 6), THF (10 mL), and either HMPA (5 drops) or TMEDA (5 drops). n-Butyllithium (0.8 mL, 1.2 M, 0.96 mmol) was added slowly to this mixture. The mixture quickly became thick. The mixture was stirred for 1 h at -40 °C and then warmed to -20 °C, and saturated aqueous ammonium chloride was added. The organic layer was separated, washed with brine and water, and dried over molecular sieves (4 A). After filtration, the solvent was removed by evaporation under vacuum 1.10 g (92% yield) of polymer was isolated. The yields of polymer ( 2%) and their spectral properties were identical regardless of whether HMPA or TMEDA was used as cocatalyst. With n-butyllithium-TMEDA, a polymer with Mw and Mn of 158,000 and 69,000, respectively, was obtained, whereas with n-butyl-lithium-HMPA, a polymer with My, and M of 120,000 and 30,400, respectively, was isolated. 

Transmetabttwn activator (2, 403). Mctalations of certain secondary benzyl-amines occur more efliciently using TMEDA-activated n-butyllithium than in mctalations with n-hutyllithium alone. Thus N-methylbenzylamine undergoes dimetalation with n-butyllithium-TMEDA predominantly at the nitrogen and o-benzyl positions. Metalation of olefins. Metalation of 1,1-dime hyl-2,2-diphenylethylene (1) with n-BuI.i-TMEDA complex gives the anion (2) in good yield as shown by the reaction... 

The reaction of vinylcyclopropanes with n-butyllithium/TMEDA leads to several lithium species 299, for example, gives mainly 300, but also 301. 

The cyclopropyl-allyl anion case itself turned out to be more of a problem. Mulvaney and Savage reacted the rruns,rruns-l,2,3-triphenylcyclopropane (316) with n-butyllithium/TMEDA which led to one (or more) of the isomeric 1,2,3-triphenylallyl anions (317). 

The case of thiobenzaldehyde dianions, which are available from benzylthiol and two equivalents of n-butyllithium-TMEDA complex, merits further comment since alkylation or allylation of these species occurs selectively at the carbanionic site and then a second alkylation can be carried out on the thiolate group (Scheme 16, entry a). ... 

Upon treatment of 1,3-pentadiyne with excess n-butyllithium/TMEDA in hexane at room temperature another lithiocarbon C,Li. 157 is obtained as was the case with... 

The principal monotrimethylsilyltoluene is the meta isomer. This agrees with the results of earlier experiments which find mainly m-lithio-toluene in the ring-lithiated byproducts in the synthesis of benzyllithium by lithiation of toluene with n-butyllithium-TMEDA (11, 12). On the basis of the current view that metalation of aromatic compounds proceeds... 

Polycyclic Aromatics. Extensive replacement of hydrogen by lithium in polycyclic aromatic hydrocarbons has been demonstrated by Halasa (15). Anthracene, biphenyl, fluorene, indene, and ferrocene (16) undergo polymetalation by n-butyllithium—TMEDA in hexane at 70°C for 24 hours. The products are insoluble mixtures of polylithio compounds containing up to 10 lithium atoms per molecule. Derivatization was accomplished using both D20 and trimethylchlorosilane and by analyzing the mixture of deuterated or silylated products by mass spectrometry. The results for anthracene, which are typical, appear in Table I. 

This ambident anion is prepared by metalation of methylenecyclobutane with the n-butyllithium-TMEDA complex (2,403 3,284 4,485-489 5, 80-86). 

The iV-(pyrrolidinomethyl) derivative of carhazole is lithiated at Cl using either r-hutyllithiiun or n-butyllithium/TMEDA. Good yields of 1-substituted carbazole can be obtained with the usual electrophiles <88JOC794>. 

Unsaturated elastomers can be readily metallated with activated organolithium compounds in the presence of chelating diamines or alkoxides of potassium or sodium. For example, polyisoprene, polybutadiene, styrene-butadiene copolymers, and styrene-isoprene copolymers can be metallated with n-butyllithium TMEDA complexes (1/1 or 1/2 ratio) to form allylic or benzylic anions. The resulting allylic anion can be employed as an initiator site to grow certain branched or comb polymer species. These polymers can include polystyrene, which would form hard domains, or polybutadiene, which forms soft domains. 

Metallation of the rings in Cr(CgHg)2 can be achieved using n-pentylsodium or the n-butyllithium.TMEDA complex. The resulting derivatives react with carbon dioxide or with aldehydes or ketones. It is difficult, however, to control the number of metal atoms which enter, so that mixtures of products are formed. 

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