Elimination butyllithium

Lithiation of thioxanthene by butyllithium and condensation with formaldehyde gives thioxanthene-9-methanol. The p-toluenesulfonyl derivative 2, on treatment with refluxing formic acid, rearranges to a dibenzotropylium ion, which gives the elimination product 3 in 44% yield.20... 

Metalated epoxides can react with organometallics to give olefins after elimination of dimetal oxide, a process often referred to as reductive alkylation (Path B, Scheme 5.2). Crandall and Lin first described this reaction in their seminal paper in 1967 treatment of tert-butyloxirane 106 with 3 equiv. of tert-butyllithium, for example, gave trans-di-tert-butylethylene 110 in 64% yield (Scheme 5.23), Stating that this reaction should have some synthetic potential , [36] they proposed a reaction pathway in which tert-butyllithium reacted with a-lithiooxycarbene 108 to generate dianion 109 and thence olefin 110 upon elimination of dilithium oxide. The epoxide has, in effect, acted as a vinyl cation equivalent. 

The synthesis of enantiomerically pure propargylic alcohols is possible using the same methodology 43b. Thus, addition of (—)-[(l-chloro-2-phenylethyl)sulfinyl]-4-methylbenzene (14) to propan-al led to a mixture of the diastereomers 15A/15B (d.r. 44 56) which are easily separated by column chromatography. After thermal elimination of the sulfinyl group the vinyl chlorides 16A/16B were obtained as a mixture of E- and Z-oleftns. Elimination of hydrogen chloride was carried out with three equivalents of butyllithium, leading to enantiomerically pure 1 -phenyl-1-pentyn-3-ol. 

Sulfinyl oxiranes 2 can be desulfurized with butyllithium at very low temperature to give oxiranes with retention of configuration as a result of a ligand exchange at sulfur (see also Table 6). However, with a benzylic substituent R1, an excess of butyllithium may at higher temperatures induce an elimination to an allylic alcohol. 

The first stable silaallene, 56, was synthesized in 1993 " " by the intramolecular attack of an organolithium reagent at the /f-carbon of a fluoroalkynylsilane (Scheme 16). Addition of two equivalents of r-butyllithium in toluene at O C to compound 54 gave intermediate 55. The a-lithiofluorosilane then eliminated lithium fluoride at room temperature to form the 1-silaallene 56, which was so sterically hindered that it did not react with ethanol even at reflux temperatures. 1-Silaallene 56 was the first, and so far the only, multiply bonded silicon species to be unreactive toward air and water. The X-ray crystal structure and NMR spectra of 56 is discussed in Sect. IVA. 

West et al. have recently described the synthesis and reactions of a 1-germaallene. Germaallene 76 (Eq. (7)) is analogous to silaallene 59a and is synthesized by intermolecular addition of f-butyllithium to precursor 75, followed by salt elimination at —78 C. This germaallene is not stable above 0 C in solution, but remains intact until heated above 90°C in the solid state. In either case, the... 

Adding butyllithium to N-silylated amines such as N-trimethylsilylaniline 1309 to form the salt 1310 and then introducing SO2 induces elimination of Me3SiOLi... 

In another example, a sequence of methylation-elimination-hydroxymethylation was used to install the functionality pattern found in the A-ring of taxol. The hydrazone dianion was generated and methylated at low temperature. The hydrazone was then deprotonated again using excess n-butyllithium and allowed to warm to room temperature, at which point formation of the vinyllithium occurred. Reaction with paraformaldehyde generated the desired product.290... 

Unlike 1,3-dithiepin anion 144a, the evidence for the instability of 145a and for the lack of aromaticity associated with lOn-electron delocalization through the sulfur atom has been reported 91,92). The reaction of the disodium salt of c/s-dimercaptoethylene (155) with either l,2-dibromo-3-propanol or l,3-dibromo-2-propanol yielded 6,7-dihydro-5f/-l,4-dithiepin-6-ol (156). Treatment of the methoxy derivative 157 derived from 156 with two equivalents of lithium dicyclohexylamide resulted in an effective elimination of methanol to give 5//-l,4-dithiepin (145) as a colorless liquid. Lithiation of 145 with n-butyllithium in tetrahydrofuran at —70 °C... 

The other important route to silenes via eliminations has been studied by Jones el al. through addition of /-butyllithium to vinylchloro- or fluorosi-lanes followed by 1,2-elimination of the LiX [Eq. (11)]. While silenes... 

Selenoaldehydes,2 In the presence of 5-10 mole% of butyllithium, this disilyl selenide converts aldehydes into selenoaldehydes with formation of the disiloxane [(CH,)3SiOSi(CH3),]. The active reagent is presumed to be lithium trimethylsilyl-selenide, (CH3)3SiSeLi, which can be regenerated by a Peterson-type elimination (equation I). 

Reaction of l,3-bis(methylthio)-2-methoxypropane with 2 moles of lithium diisopropylamide5 (or w-butyllithium) effects (a) the elimination of methanol to form l,3-bis(methylthio)propene and (b) the lithiation of this propene to generate l,3-bis(methylthio)allyllithium in solution. Its conjugate acid, l,3-bis(methylthio)propene, can be regenerated by protonation with methanol, and has also been prepared (a) in 31% yield by reaction of methylthioacetaldehyde with the lithio derivative of diethyl methylthiomethylphosphonate,5 (b) in low yield by acid-catalyzed pyrolysis of l,l-bis(methylthio)-3-methoxypropane,6 and (c) in low yield by acid-catalyzed coupling of vinyl chloride with chloromethyl methyl sulfide.7... 

The stannaphosphenes R2Sn=PAr (R = (Me3Si)2CH or 2,4,6-triisopropylphenyl, Ar = 2,4,6-tri-f-butylphenyl) can be prepared by elimination of HF across the FSn-PH unit with /-butyllithium, but no crystal structures appear yet to have been reported. Protic reagents add across the Sn=P bond, and enones, 1,2-diones, and ortho-qmnones react by [2+4] cycloaddition.593-595... 

The germaallene 194 was prepared by reaction of fluoroalkynylgermane 195 with tert-butyllithium at -78°C in about 85% yield.174 Elimination of LiF occurred at low temperature. 194 was the first allenic compound of germanium structurally characterized (Scheme 41). 

Metallation of dibenzothiophene 5-oxide with three equivalents of butyllithium followed by carbonation gave a mixture of 4-dibenzo-thiophene carboxylic acid (36 /o) and dibenzothiophene (10%). The reduction or even elimination of sulfoxide groups in the presence of... 

The LIC-KOR reagent consisting of stoichiometrically equal amounts of butyllithium ( LIC ) and potassium feri-butoxide ( KOR ) was conceived in Heidelberg and optimized in a trial-and-error effort . The fundamental idea was simple. To activate butyllithium optimally by deaggregation and carbon-metal bond polarization, a ligand was required that would surpass as an electron donor any crown ether but not suffer from the drawback of the latter, i.e. its proneness to /3-elimination. Whereas pinacolates and other v/c-diolates proved too labile to be generally useful, potassium terf-butoxide or any other bulky, hence relatively soluble, potassium or cesium alkoxide was found to serve the purpose. ... 

The Shapiro reaction occurs when a tosylhydrazone 86, easily prepared from a ketone and tosylhydrazine, is treated with 2 equivalents of an ethereal solution of n-butyllithium 87, resulting first in the removal of the N—H proton to give the anion 88 and then of a one proton from the less-substituted a position to give the dianion 89. Elimination of lithium p-toluenesulfinate in the rate-limiting step gives the lithium aUtenyldiazenide 90, which suffers loss of nitrogen to afford the alkenyllithium 91 (equation 31) ° . ... 

The proposed mechanism of this reaction is based on the nucleophilic attack of the alkyllithium compound at the carbenoid carbon atom or at the a-lithiooxy carbene. The dilithium compound 102 gives the alkene 103 by the loss of lithium oxide (equation 56). When an alkoxy residue, which is a better leaving group than U2O, is offered in the a-position of the corresponding dilithium compound, the elimination of lithium alkoxide takes place instead of lithium oxide. This is illustrated by the reaction of epoxide 104 that delivers the allylic alcohol 105 upon treatment with n-butyllithium (equation The... 

When hexachloro-1,3-butadiene (81) is reacted with four equivalents of n-butyllithium in diethyl ether, a series of lithiation and elimination reactions gives l,4-dilithio-l,3-butadiyne (82) in good yields (Scheme 30). Ijadi-Maghsoodi and Barton verified this by derivatization with various chlorosilanes in yields up to 94%". ... 

It still represents a great challenge to conduct anionic polymerizations in an automated parallel synthesizer. Above all, the technique requires an intensive purification of the reagents and the polymerization medium in order to obtain well-defined polymers. Therefore, a special procedure has been described for the inertization of the reactors [55]. It is called chemical cleaning, which is essentially rinsing all the reactors with. yec-butyllithium (.y-BuLi) prior to the reaction in order to eliminate all chemical impurities. This process can be performed in an automated manner. Due to the extreme sensitivity of the polymerization technique to oxygen, moisture, and impurities, detailed investigations on the inertization procedure and the reproducibility of the experiments need to be conducted. 

V-Methyl-2-methyl-3-(benzotriazol-l-yl)propanamide (631), on treatment with two equivalents of butyllithium, forms a dianion that reacts with alkyl and benzyl halides, aldehydes, and ketones to give monosubstituted products (632) (Scheme 124). With ethyl / -toluate, however, a lactam (634) is formed. The alkylated derivatives (632) eliminate benzotriazole upon treatment with NaOEt to afford trisubstituted a,)8-unsaturated amides (633) <93JHC1261>. 

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