NMR and calculational studies on the regioselective lithiation of 1-methoxynaphthalene

1-Methoxynaphthalene (1) undergoes regioselective lithiation in position 2 (n-BuLi/TMEDA) or in position 8 (t-BuLi), respectively. The detected formation of a n-BuLi/1 complex (1:1 n-BuLi/1 mixture) appears to have only minor influence on the regioselectivity (both products are obtained). The exchange of hydrogen atom H2 by deuterium results in a remarkably reduced reaction rate for the lithiation with n-BuLi in THF-d(8). This isotope effect and the formation of the thermodynamically less favorable 2-lithio compound suggest a kinetically controlled mechanism. The lack of an isotope effect for the reaction of 8-deuterio-1-methoxynaphthalene with t-BuLi and the formation of the thermodynamically preferred 8-lithiated product indicate a thermodynamically controlled mechanism. Slow conversion of the 2- into the 8-lithiated species (at higher temperatures) gives further evidence that n-BuLi and t-BuLi afford the kinetically and thermodynamically preferred products, respectively.     

Contrasting reactions of ketones and thioketones with alkyllithiums: a coordinated experimental and computational investigation

The reaction of ketones with organolithium reagents generally proceeds by addition of the organometallic to the electrophilic carbon of the C═O group to give the lithium salt of a tertiary alcohol. The seemingly analogous reaction of thioketones with organolithiums is a fundamentally different process: such reactions typically afford a variety of products, and addition of the organolithium to carbon of the C═S group to give a thiol is a relatively unimportant component. Reactions of the stable thioketone, adamantantanethione (1), with several alkyllithiums (MeLi, n-BuLi and t-BuLi) in a variety of solvents have been studied in the first comprehensive investigation of the reactions of organolithiums with a representative alkyl-substituted thione. Reactions of 1 with n-BuLi or t-BuLi afforded 2-adamantanethiol (2) as the major product. In an effort to explain the marked difference in behavior of ketones and thioketones in reactions with organolithiums, transition states for both the addition and reduction reactions have been located at the B3LYP/6-311+G* level using acetone and thioacetone as model substrates. The transition states for the addition of dimeric MeLi to the C═O and C═S carbons of acetone and thioacetone were significantly different as a result of the small bond angles preferred by divalent sulfur, and this accounts for the much slower addition to a C═S carbon vis-à-vis a C═O group. Transition states for reduction of acetone and thioacetone by EtLi were similar, but the greater exothermicity of the reduction of the thioketone results in an earlier transition state and lower activation energy for this process than that for the reduction of a ketone. The possible role of radical-mediated processes in this chemistry is also discussed.     

通过在线~7Li-NMR谱对负离子聚合见解的进一步验证

通过对正丁基锂(n-BuLi)/四氢呋喃(THF)引发α-甲基苯乙烯(mSt)负离子本体聚合,验证了n-BuLi缔合体可以引发聚合,形成超分子团聚体,然后在进一步聚合过程中超分子解离.证实了先前提出的负离子聚合的引发机理.通过7Li-NMR对聚合过程的在线检测,进一步证实了mSt在氘代苯为溶剂,THF为调节剂下的负离子聚合以及异戊二烯在非极性条件下的溶液聚合都存在引发剂多元缔合体向二元缔合体转变.研究还发现,少量THF可能使n-BuLi的六元缔合结构2～3个进一步串联起来,但先于六元缔合结构解离.此外,THF与n-BuLi作用,随着n-BuLi/THF的摩尔比从1∶1到1∶5的变化,可以使n-BuLi的巨大缔合体解离并向六元缔合体转变.     

Selective Halogen-Lithium Exchange Reaction of Bromine-Substituted 25,26,27,28-Tetrapropoxycalix[4]arene

Methods are described for the selective bromine-lithium exchange reaction of bromine-substituted calix[4]arenes with either n-BuLi or t-BuLi in THF. Quenching of the lithiated calix[4]arenes with MeOH, D(2)O, CH(3)SSCH(3), B(OCH(3))(3), DMF, or CO(2) as electrophiles resulted in 5-monosubstituted, 5,17-disubstituted, or 5,11,17,23-tetrasubstituted calix[4]arenes with H, D, SCH(3), B(OH)(2), CHO, or COOH functionalities.     

Aryl- and alkenyllithium preparations and copper-catalyzed reaction between the derived magnesium reagents and the monoacetate of 4-cyclopentene-1,3-diol

[reaction: see text] Aryl- and alkenyllithiums, prepared by halogen-lithium exchange with lithium, exchange with n-(or t-)BuLi, stannane-lithium exchange with n-BuLi, and direct lithiation with n-BuLi, were transformed into magnesium reagents with MgCl2 and subjected to CuCN-catalyzed reaction with the title monoacetate. Except for the halogen-lithium exchange with n-BuLi, the other preparations of the lithium anions were found to be compatible with the CuCN-catalyzed reaction to afford S(N)2-type products efficiently.     

Aminoalkoxide-mediated formation and stabilization of phenylpyridyllithium: straightforward access to phenylpyridine derivatives

It is shown that lithium aggregates promoted the efficient metalation of phenylpyridines and stabilization of phenylpyridyllithium. The BuLi-LiDMAE superbase prevented dimerization or nucleophilic addition encountered with t-BuLi or n-BuLi. The reported selective pyridine ring lithiation of 2-, 3-, and 4-phenylpyridine alpha to nitrogen opens a straightforward access to their derivatives.     

High yield acyl anion trapping reactions: direct nucleophilic acylation of isocyanates and isothiocyanates.

The reactions of t-BuLi, sec-BuLi and n-BuLi with CO in the presence of isothiocyanates and isocyanates gives, after hydrolytic work-up, α-oxothioamides, RC(O)C(S)NHR′, and α-oxoamides, RC(O)C(O)NHR′, respectively, in good yield. Competition from the direct reaction of RLi with the substrate is encountered only in the case of reactions of the n-BuLi/CO system with isocyanates.     

两步合成法对SBS结构与性能的研究

<正> 以单官能团烷基锂为引发剂,用两步法合成苯乙烯-丁二烯-苯乙烯(SBS)嵌段共聚物文献中仅见一般性介绍,较为详细的只有Cunningham的研究报告,据认为用n-BuL(正丁基锂)为引发剂时共聚物的物性不佳。我们以环己烷为溶剂,n-BuLi为引发剂,对两步法合成SBS进行了研究。由于在系统中引入了少量THF(四氢呋喃),并找到了消除体系中微量杂质的有效方法,因而试验重复性好,产品物性优良,超过文献值而与Shell公司偶联法工业化产品相近。     

TMSCl促进的分子内亲核取代反应合成α-亚烷基-哌啶酮

以烯基碘代物为底物,丁基锂为锂代试剂,THF为溶剂,在TMSCl促进下通过分子内亲核取代反应合成了4个α-亚烷基-哌啶酮(2a~2d),其结构经~1H NMR,~(13)C NMR和HR-MS(ESI)确证。在最优反应条件(1 2 mmol,n-Bu Li 2.4 mmol,TMSCl 3 mmol,THF 20 m L,于170℃反应1 h)下,2a~2d收率68%~84%。     

Solvent and temperature effects on the reduction and amination reactions of electrophiles by lithium dialkylaminoborohydrides

The influence of temperature and solvent effects on the reduction and amination mechanisms of iodomethane by lithium N,N-diisopropylaminoborohydride (iPr-LAB) was examined in varying concentrations of THF and dioxane. The reactions of benzyl chloride and trimethylsilyl chloride with iPr-LAB in THF were also studied. The amination of iodomethane is favored over reduction at low and room temperatures in pure THF and with increasing the amount of dioxane in THF. At higher temperatures, the reduction reaction appears to compete with the amination. In dioxane solvent, however, iodomethane yields exclusively the amination product regardless of temperature. On the other hand, reduction by iPr-LAB to the aminoborane is the only product observed in THF when benzyl chloride and trimethylsilyl chloride are used. To understand the solvent effects on the product distribution, ab initio and density functional theory (DFT) calculations were used to examine the mechanisms of reduction and amination of chloromethane and bromomethane by lithium dimethylaminoborohydride (LAB) in THF and dioxane. The results of these calculations show that the relative reaction barrier heights are significantly affected by the nature of the coordinated solvent molecule and thus lend support to the experimental observations.     

A monolithiated and its related 1,3-dilithiated allylsilane: syntheses, crystal structures, and reactivity

Treatment of Me2Si(CH2CH=CH2)(CH2NC5H10) with 1 or 2 equiv of t-BuLi afforded the mono- or dilithiated allylsilanes, which crystallize as a tetramer and a hexamer from pentane. The product selectivity in trapping reactions is influenced by the ability of both the solvent and the electrophile to coordinate the lithium center.     

Optimizing the Synthesis of Tetratellurafulvalene

A systematic synthetic study of the pi-donor tetratellurafulvalene (TTeF, 6) has resulted in an optimized preparation producing repeatable yields of over 20%. The use of a "one-step" Li/Sn metal exchange/Te(0) insertion procedure and freshly prepared microcrystalline Te(0) serve to drive toward products, the equilibria converting (Z)-1,2-bis(trimethylstannyl)ethylene (1) to its corresponding metal-exchanged vinyllithium species and subsequently to lithium ditellurolate 5. Furthermore, the use of LiCl as an additive to enhance the reactivity of n-BuLi in these metal exchange reactions also increases yields and reproducibility. The slow addition of 1 equiv of tetrahaloethylene during the final cyclization step favors intramolecular reactions which produce TTeF vs intermolecular reactions that lead to oligomeric byproducts. The use of tetrabromoethylene in place of tetrachloroethylene in this step also reduces byproduct formation.     

Structure of n-butyllithium in mixtures of ethers and diamines: influence of mixed solvation on 1,2-additions to imines

n-BuLi in diamine/dialkyl ether mixtures forms ensembles of hetero- and homosolvated dimers. Solutions in TMEDA/THF (TMEDA = N,N,N',N'-tetramethylethylenediamine) are not amenable to detailed investigation because of rapid ligand exchange. TMCDA/THF mixtures (TMCDA = trans-N,N,N',N'-tetramethylcyclohexanediamine) afford clean assignments for a mixture of homo- and heterosolvated dimers but demonstrate poor control over structure. TMCDA/tetrahydropyran (THP) mixtures and TMEDA/Et2O mixtures afford clean structural assignments as well as excellent structural control. Rate studies of the 1,2-addition of n-BuLi using TMCDA/THP mixtures reveal cooperative solvation in which both THP and TMCDA coordinate to lithium at the monomer- and dimer-based transition structures. The two mechanisms are affiliated with markedly different stereochemistries of the 1,2-addition to imines. The results show strong parallels with previous investigations of 1,2-additions in TMEDA/Et2O mixtures.     

无过渡金属参与下茚并-[1,2-b]吲哚-10(5H)-酮的合成

发展了一种从3-(2-溴代苯甲酰基)-吲哚出发在无过渡金属参与下合成茚并吲哚酮类化合物的新方法。在甲苯/四氢呋喃(2∶1)混合溶剂中,3-(2-溴代苯甲酰基)-吲哚、正丁基锂和碘化锌原位生成的2-吲哚锌在碘化锂辅助下与芳基溴化物发生分子内加成-环化反应,合成了一系列取代的茚并-[1,2-b]吲哚-10(5H)-酮类化合物,且均获得了较好的收率。考察了溶剂、卤化锌、添加剂对产率的影响。     

Sila-metalation route to hydrido(trialkylsilyl)silyllithiums

The proton abstraction (sila-metalation) of trialkylsilyl-substituted dihydridosilanes with t-BuLi or LDA in THF was found to be a convenient route to the corresponding silyllithiums (RR'SiHLi; 1a, R, R' = t-BuMe(2)Si; 1b, R, R' = Me(3)Si; 1c, R, R' = i-Pr(2)MeSi; 1d, R = t-BuMe(2)Si, R' = 4-methylphenyl). Hydridosilylithium 1a was isolated as air- and moisture-sensitive, but thermally stable, colorless crystals. X-ray analysis has shown that 1a is dimeric in the solid state, where two lithium atoms bridge between anionic silicon atoms forming a parallelogram, each lithium atom is coordinated by one THF molecule, and the Si-H hydrogen atoms are in the plane of the parallelogram. X-ray analysis has shown that (t-BuMe(2)Si)(2)GeHLi (5) has a dimeric structure similar to that of 1a.     

Some aspects of anionic butadiene copolymerization

The relationship between ideal copolymerization behavior and the nature of reactive species in butyllithium (n-BuLi) initiated anionic copolymerization of styrene (St)- butadiene (Bd) in nonpolar solvent has been discussed. The monomer reactivity ratios (m.r.r.) for various reactive species were evaluated by kinetic study and statistical approach (using ¹³C NMR data) in St-Bd anionic copolymerization system with THF as polar additive. The Markovian mechanisms for different propagating reactions in this complex copolymerizing system have been postulated. Furthermore, “pseudo” zero order Markovian mechnism could be sophisticatedly established in the n-BuLi/tertiary amyloxy potassium (t-AmOK)/THF initiated St-Bd copolymerization system, provided that the apparent rate constants of both monomers are equal. Thus, by adjusting the ratio of K/Li and THF/Li, copolymers with composition almost identical to the ratio of initial monomer feed composition at different stages of conversion could be obtained.     

Synthesis, molecular structure, and reactivity of the isolable silylenoid with a tricoordinate silicon

The first tricoordinate fluorosilylenoid, (t-Bu2MeSi)2SiFLi.3THF (1), was synthesized, and its X-ray molecular structure was determined. 1 was synthesized in 40% yield by a bromine-lithium exchange reaction in THF of the corresponding fluorobromosilane with t-Bu2MeSiLi. 1 is best described as an R2SiF- anion attracted to a (Li.3THF)+ cation with a small contribution of resonance structure that consists of a silylene fragment and FLi.3THF. 1 reacts as a nucleophile with MeCl, PhH2SiCl, H2O, and MeOH, as an electrophile with MeLi, and as a silylene with Li (or t-BuLi) and Na, yielding alpha-lithium and alpha-sodium silyl radicals, respectively. Either photolysis or thermolysis of 1 yields the corresponding disilene R2Si=SiR2 (R = t-Bu2MeSi), probably via dimerization of R2Si:.     

Synthesis of diastereomerically and enantiomerically pure 2,3-disubstituted tetrahydrofurans using a sulfoxonium ylide

Nucleophilic substitution reactions of 2,3-epoxy alcohols, easily prepared via Sharpless asymmetric epoxidation chemistry, offer access to a wide variety of enantiomerically pure compounds. In this communication, we describe the use of a Payne rearrangement to control regioselectivity in the ring-opening of a series of 2,3-epoxy alcohols with dimethylsulfoxonium methylide to yield diastereomerically and/or enantiomerically pure disubstituted tetrahydrofuran rings. The factors influencing the success and substitution pattern of the THF ring products are discussed, including steric, electronic, and solvent effects.     

钐(II)类卡宾CH_3SmCH_2I与乙烯环丙烷化反应及溶剂化效应(THF)对反应途径影响的理论研究

用密度泛函B3LYP方法研究了过渡金属钐类卡宾与乙烯的环丙烷化反应的机理.对钐类卡宾试剂CH3SmCH2I和CH2CH2反应的反应物、中间体、过渡态和产物构型的全部结构几何参数进行了优化,并计算了THF溶液的溶剂化效应,用内禀反应坐标(IRC)计算和频率分析方法,对过渡态进行了验证.结果表明:CH3SmCH2I与CH2CH2环丙烷化反应按亚甲基转移机理(通道A)和卡宾金属化机理(通道B)都可以进行,与锂类卡宾的反应机理相同,通道A比通道B反应的势垒降低了14.65kJ/mol.溶剂化效应使通道B比通道A的反应势垒大幅度提高,更有利于反应沿通道A进行,而不利于通道B.     

Lithium–Bromide Exchange versus Nucleophilic Addition of Schiff's base: Unprecedented Tandem Cyclisation Pathways

By exploring lithium–bromide exchange reactivity of aromatic Schiff's bases with tert-butyllithium (tBuLi), we have revealed unprecedented competitive intermolecular and intramolecular cascade annulation pathways, leading to valuable compounds, such as iso-indolinones and N-substituted anthracene derivatives. A series of reaction parameters were probed, including solvent, stoichiometry, sterics and organolithium reagent choice, in order to understand the influences that limit such ring-closing pathways. With two viable reactivity options for the organolithium on the imine; namely, nucleophilic addition or lithium–bromide exchange, a surprising competitive nature was observed, where nucleophilic addition dominated, even under cryogenic conditions. Considering the most commonly used solvents for lithium–bromide exchange, tetrahydrofuran (THF) and diethyl ether (Et₂O), contrasting reactivity outcomes were revealed with nucleophilic addition promoted in THF, while Et₂O yielded almost double the conversion of cyclic products than in THF.