Butyllithium interconversions

Halogen-metal interconversion between bromothiophenes and n-butyllithium, leading to thienyllithium derivatives and n-butyl bromide, occurs almost instantaneously and in very high yield even at... 

When the bromothiophenes and n-butyllithium are reacted at room temperature, halogen-metal interconversion and metalation occur concurrently to different degrees, and mixtures are obtained. ... 

Thiophenedithiol (170) has been prepared by halogen-metal interconversion between the lithium salt of 4-bromo-3-thiophenethiol and n-butyllithium at —70°C, followed by reaction with sulfur/ IR, NMR, and UV spectra showed that this compound exists in the dithiol form (170). The compound obtained as a by-product in the... 

Bromo- and iodoarenes are the oldest and most typical substrates for permutational halogen/metal interconversions. Butyllithium is routinely used for this purpose (Table 16). Hetero-substituents such as dialkylamino or bis(trialkylsilyl)amino, cyano or nitro (Table 17), alkoxy and 2-tetrahydropyranyloxy (Table 18), lithiooxy or lithiooxycarbonyl (Table 19) and fluoro or trifluoromethyl (Table 20) and chloro, bromo or iodo (Table 21) are well tolerated. 

Halogen-metal interconversion between bromothiophenes and n -butyllithium occurs almost instantaneously and in very high yield. The reaction with 3-bromothiophene is usually carried out at -70 °C to avoid any (rans-lithiation. When bromine-lithium exchange takes place, steric crowding in the molecule decreases. As a consequence the percentage of 2-lithio derivative in relation to the 5-lithio isomer formed from 3-alkyl-2,5-... 

With increasing temperature above 185 K and with increasing concentration of the n-butyllithium, the authors reported progressive averaging of the 13C—6Li coupling constant of dimers as well as of the resonances of dimer with tetramer. A line shape analysis of the 13C NMR of lithium bound carbon, using our PI method, best took account of the interconversion of tetramers with dimers via a degenerate process (equation 75),... 

A common theme in many reactions is the generation of an equivalent of CP2M through the reduction of a tetravalent precursor metallocene with a metal alkyl such as n-butyllithium. The chemistry of olefin complexes of CP2M is characterized by a facile interconversion between formally M(II) and M(IV) manifolds, as shown in equation 34. Another central motif of metallocene chemistry, especially that of titanocenes, is the accessibility of pathways connecting metallacycles and metal alkylidene complexes, eg in alkene metathesis (eq. 35). 

The halogen-metal exchange or interconversion reaction was independently discovered by us and by G. Wittig. In one of our initial reactions we observed that o-bromoanisole reacted with n-butyllithium to yield o-anisyllithium and -butyI bromide. 

Halogen/metal permutation and hydrogen/metal permutation (usually apostrophed as "metalation") dominate the interconversion methods. They employ organoalkali reagents such as phenyllithium, methyllithium, -butyllithium, iec-butyllithium, or the superbasic LIC-KOR mixture. However, even if commercial, these reagents have to be made beforehand. The reaction of a chloro- or bromo-substituted hydrocarbon with lithium, sodium, or magnesium offers a standard entry to them. Thus, ultimately one always has to revert to the metal. 

Johann Mulzer and Benjamin List " advocate the replacement of tinoxy derivatives by trimethylsilyloxy analogs. A direct silyl/lithium interconversion is assumed to preceed the rearrangement when an intermediate such as 370 (Scheme 1-288) is treated with a large excess of -butyllithium. However, an alternative pathway initiated... 

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