Lithium In THF Research Articles

A novel approach to l-tryptophan grafting on mesoporous MCM-41: A recoverable heterogeneous material for organocatalyzed benzo[N,N]-heterocyclic condensation

An unprecedented strategy has been developed to introduce l-tryptophan into MCM-41 by binding the indolic NH group of l-tryptophan to modified MCM-41, resulting in the creation of l-Tryp-N-pMCM-41. Initially, 3-Cl-pMCM-41 was prepared by modifying activated MCM-41 with 3-chloropropyltrimethoxysilane. Subsequently, the covalent attachment between the indolic NH group of l-tryptophan and 3-Cl-pMCM-41 was achieved using n‑butyl lithium in THF at -78 °C under an argon atmosphere. l-Tryp-N-pMCM-41 has been characterized by FT-IR, XRD, TGA, EDS, BET and nitrogen physisorption measurements. The organocatalytic performance of this chemically stable material was assessed in the synthesis of both symmetrical and unsymmetrical quinoxalines. The reaction involved the condensation of a series of aromatic 1,2-diamines with 1,2-diketones in methanol at room temperature. Overall, the organocatalytic reaction proceeded smoothly to afford the corresponding quinoxalines in moderate to excellent yields. Furthermore, the crystal structure of an unsymmetrical quinoxaline has been determined by single crystal X-ray diffraction. This metal-free procedure offers several noteworthy advantages, including the simplicity of the reaction, minimal catalyst usage, recyclability of the catalyst and environmentally friendly characteristics. Moreover, this green heterogeneous organocatalyst is a suitable candidate for preparing various valuable pharmaceutical compounds under ambient conditions avoiding the use of strong acids and without any possibility of metal contamination.

Revisiting the Schlenk dimerisation reaction of 1,1-diphenylethene

The reaction between 1,1-diphenylethene and two equivalents of lithium in THF gave the complex [(Ph2CCH2CH2CPh2)Li2(THF)4] (3), which crystallised from Et2O/THF as the dialkyllithate salt [Li(THF)4][(Ph2CCH2CH2CPh2)Li(THF)] (3a). A similar reaction between 1,1-diphenylethene and sodium metal in THF gave [(Ph2CCH2CH2CPh2)Na2(THF)1.5] (4), which crystallised from THF as the polymer [(Ph2CCH2CH2CPh2)Na2(THF)3]∞ (4a). In contrast, reactions between 1,1-diphenylethene and potassium under the same conditions gave intractable mixtures of products. However, treatment of 3 with two equivalents of KOtBu in THF yielded the complex [(Ph2CCH2CH2CPh2)K2(THF)0.5] (5) as a deep red powder; treatment of 5 with two equivalents of 12-crown-4, followed by crystallisation from methylcyclohexane/THF, gave the adduct [(Ph2CCH2CH2CPh2)K2(THF)2(12-crown-4)2] (5a). A similar reaction between 3 and 12-crown-4 gave the separated ion pair [Li(THF)(12-crown-4)][Li(THF)0.5(OEt2)0.5(12-crown-4)](Ph2CCH2CH2CPh2) (3b), which contains the free 1,1,4,4-tetraphenyl-1,4-butanediide dicarbanion. X-ray crystallography revealed that the C3C centres of the ligands adopt a near planar geometry, irrespective of whether a metal cation is in close contact.

12-Vertex Zwitterionic Bis-phosphonium-nido-carborates through Ring-Opening Reactions of 1,2-Diphosphetanes.

Carborane-substituted 1,2-diphosphetanes (Ia,b) react with elemental lithium in THF with cleavage of the P-P bond to give a deep red solution from which, in the case of Ia, red crystals of a lithiated intermediate, [{1-Li(THF)PtBu-6-PtBu-4,1,6-closo-Li(THF)C2 B10 H10 }{Li(THF)3 }]2 ⋅2 THF (2 a), are obtained. The compound is dimeric, C2 -symmetric and contains six lithium and four phosphorus atoms. Two lithium atoms cap the six-membered C2 B4 faces, resulting in two 13-vertex closo-clusters (according to Wade's rules) with docosahedral geometry. The addition of methyl iodide resulted in the formation of zwitterionic bis-phosphonium-nido-carborates 7,10-bis(tert-butyldimethylphosphonium)dodecahydro-7,10-dicarba-nido-dodecaborate(2-) (1 a) and 7,10-bis(N,N-diisopropylaminodimethylphosphonium)dodecahydro-7,10-dicarba-nido-dodecaborate(2-) (1 b) in moderate to good yields. Compounds 1 a and 1 b exhibit short Ccluster -P bonds and large Ccluster ⋅⋅⋅Ccluster distances in the solid state. Further insight into the ring opening and reduction potential of the alkyl halide was obtained from methylation reactions of different 1,2-bis-phosphinocarboranes. The reaction of rac-/meso-1,2-bis(tert-butylmethylphosphino)-1,2-dicarba-closo-dodecaborane(12) (3 a) with two equivalents of methyl iodide also resulted in the formation of 1 a (as shown by NMR spectroscopy), whereas the reaction of 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane(12) with methyl triflate afforded the phosphonium salt 1-methyl-diphenylphosphonium-2-diphenylphosphino-1,2-dicarba-closo-dodecaborane(12) triflate (4) without reduction of the cluster.

The Chemistry of ortho-(Diarylphosphino)aryl Isocyanides

The title phosphine-isocyanides were obtained by reaction of 2-lithioaryl isocyanides with diarylchlorophosphines. They cyclize to 1,3-benzazaphospholes with cleavage of their two aryl–P bonds upon treatment with an excess of lithium in THF. Their P═CH2 ylids spontaneously evolve to give λ5-1,4-benzazaphosphinines. Their complexation by gold(I), palladium(II), and nickel(II) chlorides has been investigated. An original pincer diphosphine–carbene complex has been obtained with palladium. The new products have been characterized by X-ray crystal structure analysis.

Synthesis and NMR-Study of the 2,3,4,5-Tetraethylsilole Dianion [SiC4Et4]2−•2[Li

The previously unknown silole dianion [SiC4Et4]2−•2[Li]+ (3) was prepared by the sonication of 1,1-dichloro-2,3,4,5-tetraethyl-1-silacyclopentadiene [Cl2SiC4Et4, 2] with more than four equivalent of lithium in THF. 1H-, 13C-, and 29Si-NMR data of 3 are compared with those of the reported silole dianion [SiC4Ph4]2−. Trapping of 3 with trimethylchlorosilane gave 1,1-bis(trimethylsilyl)-2,3,4,5-tetraethyl-1-silacyclopentadiene [(Me3Si)2SiC4Et4, 4] in high yield. The silole of 2 was synthesized in high yield in three steps by a modified procedure using Cp2ZrCl2 via Cp2ZrC4Et4 and 1,4-dibromo-1,2,3,4-tetraethyl-1,3-butadiene.

Dilithio 9,10-Diborataanthracene: Molecular Structure and 1,4-Addition Reactions

9,10-Dihydro-9,10-diboraanthracene ([1]n) and its SMe2 adduct 1(SMe2)2 are readily reduced with lithium in THF to the dianionic 9,10-diborataanthracene Li2[1]. An X-ray crystal structure analysis of (Li(thf)2)2[1] revealed monomeric inverse sandwich complexes, each of them containing two Li(thf)2 moieties coordinated to both sides of the central B2C4 ring. Compared to 9,10-dimethyl-9,10-dihydro-9,10-diboraanthracene, the four B−CAr bonds of (Li(thf)2)2[1] are shorter by 0.046(4) Å, thereby indicating an increased degree of B═CAr double-bond character. Consequently, (Li(thf)2)2[1] reacts with 4,4′-dimethylbenzophenone as a B═CAr−CAr═B diene and undergoes a [4+2] cycloaddition reaction with formation of a bicyclic product. In contrast, tert-butylacetylene reacts with (Li(thf)2)2[1] under formal 1,4-addition of its methinic C−H group instead of its C≡C triple bond to the two boron atoms.

N-Heterocyclic Germylidenide and Stannylidenide Anions: Group 14 Metal(II) Cyclopentadienide Analogues

The reaction of a sterically bulky β-diketiminato lithium complex [Li(ButNacnac)] (ButNacnac = [{N(Dip)C(But)}2CH]−, Dip = C6H3Pri2-2,6) with GeCl2·dioxane has given the germanium(II) chloride complex [(ButNacnac)GeCl] (3). Both it and its known tin analogue, [(ButNacnac)SnCl] (4), were crystallographically characterized and found to be monomeric in the solid state. The reduction of both complexes with elemental lithium in THF led to lithium complexes of N-heterocyclic germylidenide and stannylidenide anions, viz., [(THF)Li{η5-EC(But)C(H)C(But)N(Dip)}] (E = Ge, 5; Sn, 6). The reduction of the germanium(II) precursor, 3, also afforded the germanium(II) amide complex [(ButNacnac)Ge{N(H)(Dip)}] (7). The mechanisms of formation of the complexes are thought to involve a number of steps, including reductive ring contraction reactions. The crystallographic and spectroscopic data for [(THF)Li{η5-EC(But)C(H)C(But)N(Dip)}] indicate a significant degree of aromatic π-delocalization within their heterocycles.

Synthesis of 1‐Methyl‐6,10‐diphenylheptalene Derivatives

AbstractThe reduction of heptalene diester 1 with diisobutylaluminium hydride (DIBAH) in THF gave a mixture of heptalene‐1,2‐dimethanol 2a and its double‐bond‐shift (DBS) isomer 2b (Scheme 3). Both products can be isolated by column chromatography on silica gel. The subsequent chlorination of 2a or 2b with PCl5 in CH2Cl2 led to a mixture of 1,2‐bis(chloromethyl)heptalene 3a and its DBS isomer 3b. After a prolonged chromatographic separation, both products 3a and 3b were obtained in pure form. They crystallized smoothly from hexane/Et2O 7 : 1 at low temperature, and their structures were determined by X‐ray crystal‐structure analysis (Figs. 1 and 2). The nucleophilic exchange of the Cl substituents of 3a or 3b by diphenylphosphino groups was easily achieved with excess of (diphenylphospino)lithium (=lithium diphenylphosphanide) in THF at 0° (Scheme 4). However, the purification of 4a/4b was very difficult since these bis‐phosphines decomposed on column chromatography on silica gel and were converted mostly by oxidation by air to bis(phosphine oxides) 5a and 5b. Both 5a and 5b were also obtained in pure form by reaction of 3a or 3b with (diphenylphosphinyl)lithium (=lithium oxidodiphenylphospanide) in THF, followed by column chromatography on silica gel with Et2O. Carboxaldehydes 7a and 7b were synthesized by a disproportionation reaction of the dimethanol mixture 2a/2b with catalytic amounts of TsOH. The subsequent decarbonylation of both carboxaldehydes with tris(triphenylphosphine)rhodium(1+) chloride yielded heptalene 8 in a quantitative yield. The reaction of a thermal‐equilibrium mixture 3a/3b with the borane adduct of (diphenylphosphino)lithium in THF at 0° gave 6a and 6b in yields of 5 and 15%, respectively (Scheme 4). However, heating 6a or 6b in the presence of 1,4‐diazabicyclo[2.2.2]octane (DABCO) in toluene, generated both bis‐phosphine 4a and its DBS isomer 4b which could not be separated. The attempt at a conversion of 3a or 3b into bis‐phosphines 4a or 4b by treatment with t‐BuLi and Ph2PCl also failed completely. Thus, we returned to investigate the antipodes of the dimethanols 2a, 2b, and of 8 that can be separated on an HPLC Chiralcel‐OD column. The CD spectra of optically pure (M)‐ and (P)‐configurated heptalenes 2a, 2b, and 8 were measured (Figs. 4, 5, and 9).

Synthesis and structural characterisation of alkali metal complexes of heteroatom-stabilised 1,4- and 1,6-dicarbanions

A straightforward Peterson olefination reaction between either [{(Me(2)PhSi)(3)C}Li(THF)] or in situ-generated [(Me(3)Si)(2){Ph(2)P(BH(3))}CLi(THF)(n)] and paraformaldehyde gives the alkenes (Me(2)PhSi)(2)C[double bond, length as m-dash]CH(2) () and (Me(3)Si){Ph(2)P(BH(3))}C[double bond, length as m-dash]CH(2) (), respectively, in good yield. Ultrasonic treatment of with lithium in THF yields the lithium complex [{(Me(2)PhSi)(2)C(CH(2))}Li(THF)(n)](2) (), which reacts in situ with one equivalent of KOBu(t) in diethyl ether to give the potassium salt [{(Me(2)PhSi)(2)C(CH(2))}K(THF)](2) (). Similarly, ultrasonic treatment of with lithium in THF yields the lithium complex [[{Ph(2)P(BH(3))}(Me(3)Si)C(CH(2))]Li(THF)(3)](2).2THF (). The bis(phosphine-borane) [(Me(3)Si){Me(2)(H(3)B)P}CH(Me(2)Si)(CH(2))](2) () may be prepared by the reaction of [Me(2)P(BH(3))CH(SiMe(3))]Li with half an equivalent of ClSiMe(2)CH(2)CH(2)SiMe(2)Cl in refluxing THF. Metalation of with two equivalents of MeLi in refluxing THF yields the lithium complex [[{Me(2)P(BH(3))}(Me(3)Si)C{(SiMe(2))(CH(2))}]Li(THF)(3)](2) (), whereas metalation with two equivalents of MeK in cold diethyl ether yields the potassium complex [[{Me(2)P(BH(3))}(Me(3)Si)C{(SiMe(2))(CH(2))}](2)K(2)(THF)(4)](infinity) () after recrystallisation. X-Ray crystallography shows that, whereas the lithium complex crystallises as a discrete molecular species, the potassium complexes and crystallise as sheet and chain polymers, respectively.

Homologues of N-heterocyclic carbenes: Detection and electronic structure of N-bridgehead pyrido[ a]-anellated 1,3,2-diazagermol-2-ylidenes

Novel N-bridgehead pyrido[ a]-anellated 1,3,2-diazagermol-2-ylidenes 1a, b were obtained from GeCl 2 · dioxane and dilithium reagents formed from N- tert-butyl pyridine-2-aldimines and excess lithium in THF whereas attempts to generate the analogous silylene by reduction of the dichloro-pyrido[ a]-1,3,2-diazasilole 4a, synthesized from SiCl 4 and the new dilithium reagent, failed. Characteristic chemical shifts of the pyrido 1H and 13C nuclei between those of pyridine compounds and the not fully cyclodelocalized electron-rich 4a with dihydropyridine substructure hint to a cyclodelocalized 10π electron system in 1a, b. Quantum chemical investigations of a series of pyrido[ a]- and benzo-anellated imidazol-2-ylidenes and their silylene and germylene homologues show for all compounds cyclodelocalized 10π-systems but for pyrido[ a]-anellation an increase of the energy of the π-MO’s relative to those of element(II) lone electron pairs which leads to destabilization compared to the benzo-anellated isomers.

Diazadienes in lanthanide chemistry: a new insight into old ligands. Synthesis, structures, and properties of complexes {[(R)CNC6H3Pri 2]2}Lu(THF)2(μ-Cl)2Li(THF)2 (R = CH3 or CH2)

The reaction of the dianionic derivative [DADLi2] (DAD is 1,4-bis(2,6-diisopropylphenyl)-2,3-dimethyl-1,4-diazabuta-1,3-diene), which was synthesized in situ by reduction of the corresponding DAD with an excess of metallic lithium in THF, with anhydrous LuCl3 (1: 1) affords the metallacyclic complex {[(Me)CNC6H3Pri2]2}Lu(THF)2(μ-Cl)2Li(THF)2 (1) containing the enediamide fragment N-C(Me)=C(Me)-N. The treatment of DAD with 2 equiv. of BuLi in a diethyl ether-hexane mixture at 20 °C results in the C-H bond activation of the methyl substituents at the imine carbon atom. The reaction of the in situ formed dilithium derivative [DAD−2HLi2] with LuCl3 in THF afforded the complex {[(CH2)CNC6H3Pri2]2}-Lu(THF)2(μ-Cl)2Li(THF)2 (2) with the diamide ligand N-C(=CH2)-C(=CH2)-N. The structures of complexes 1 and 2 were established by X-ray diffraction.

Synthesis and Characterization of the Monomeric Vicinal Dianion Li2(THF)3[ArNC(SiMe3)2] and the Aluminum and Lithium Derivatives of the Amido Ligand [ArNCH(SiMe3)2]−

Reaction of the imine ArNC(SiMe3)2 (1; Ar = 2,6-iPr2C6H3) with LiAlH4 in THF resulted in the formation of the dimeric hydroaluminate [(THF)2LiH3AlL]2 (2; L = [ArNCH(SiMe3)2]−). 2 reacted with CH3I to give the monomeric aluminum dihydride LAlH2(THF) (3), which can be converted to the diiodide LAlI2(THF) (4) upon treatment with 2 equiv of Me3SiI. The quasi two-coordinate lithium amide Li(OEt2)L (8) with an intramolecular CH−Li interaction was obtained by the deprotonation of the corresponding amine LH (5) generated from hydrolysis of 2. Reduction of 1 with lithium in THF resulted in the first structurally characterized monomeric C−N vicinal dianion, Li2(THF)3[ArNC(SiMe3)2] (6), and the monomeric lithium amide Li(THF)2L (7).

Allylation Reactions of Aromatic Aldehydes and Ketones with Lithium in THF under Ultrasonic Irradiation.

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Reductive dearomatization of biphenyl: sequential one-pot regioselective introduction of two different electrophiles

The reaction of biphenyl ( 1) with an excess of lithium in THF at room temperature leads to a solution of the corresponding dianion ( I), which by successive reactions with an alkyl fluoride [E 1 = n-C 8H 17F, c-C 5H 9CH 2F, CH 2 CH(CH 2) 4F] at 0 °C and another electrophile [E 2 = n-C 4H 9Br, Et 2CO, Me 2C(O)CH 2, i-Pr 3SiCl] at −78 °C yields the corresponding 1,4-disubstituted 1,4-dihydrobiphenyls 3 in a regioselective manner, as mixtures of cis- and trans-isomers. The diastereomers of 3 are separated by column chromatography.

Allylation Reactions of Aromatic Aldehydes and Ketones with Lithium in THF under Ultrasonic Irradiation

The allylation reactions of aromatic aldehydes and ketones were carried out in 69–90% yield using Li–THF system under ultrasound irradiation at r.t. for 40 min. The reactions of the same system with stirring gave homoallyl alcohols in 49–67% yield at r.t. for 4 h.

Dilithium 1,4-Disilacyclohexa-2,5-diene-1,4-diide by the Reduction of 1,4-Disilabicyclo[2.2.0]hexa-2,5-diene: Synthesis and Characterization

The dilithium 1,4-bis(di-tert-butylmethylsilyl)-2,3,5,6-tetraethyl-1,4-disilacyclohexa-2,5-diene-1,4-diide compound 22-·2[Li+(thf)] was prepared by the reduction of 1,4-bis(di-tert-butylmethylsilyl)-2,3,5,6-tetraethyl-1,4-disilabicyclo[2.2.0]hexa-2,5-diene (1) with lithium in THF. 22-·2[Li+(thf)] has a boat conformation of its six-membered ring with a folding angle of 124.0°.

Chemo-reductive silylation of hypersilyl arenes – Unusual cleavage of an aromatic C[dbnd]C double-bond

The new compounds 1,1,6,6-tetrakis(trimethylsilyl)-3-tris(trimethylsilyl)silyl-hexa-2,4-diene (3) and 2,4,6-trimethyl-3,4-bis(trimethylsilyl)-1-tris(trimethylsilyl)silyl-cyclohexa-1,5-diene (4b) have been isolated as by-products from the reaction of PhSiCl3 or MesSiCl3 with Me3SiCl and lithium in THF at low temperatures. The X-ray crystal structures of 3 and 4b are reported.

Solid-Phase Synthesis of a Combinatorial Cross-Conjugated Dienone Library

The solid-phase synthesis of a combinatorial library of cross-conjugated dienones and the biological activity of the library members are described. Reaction of cyclopentenone 1 with 3-trimethylsilyl-2-propynyl lithium in THF at -78 °C gave diol 2 in 85% yield as a single isomer. Removal of the TMS group under basic conditions and selective oxidation of the secondary alcohol gave cyclopentenone 3 in 65% yield. Cyclopentenone 3 was anchored onto the 3,4-dihydro-2H-pyran polystyrene to give solid-supported 4-propynyl-4-hydroxylcyclopentenone 4 as a key intermediate. A 96-member combinatorial synthesis using the Sonogashira coupling reaction of 4 with 12 halides (5a-l) and aldol condensation of 6a-l with eight aldehydes 7A-H led to 74 cross-conjugate dienones 9 (yield: 55-137%, purity: 11-97%).

Investigations on 2,3′-Biquinolyl. 16. The Regioselectivity of Reduction of 1-Alkyl-3-(2-quinolyl)quinolinium and 1,1′-Dialkyl-3,3′-di(2-quinolyl)-1,1′,4,4′-biquinolyl Iodides Using Metallic Zinc, Lithium and Potassium

The reaction of 1-alkyl-3-(2-quinolyl)quinolinium iodides with excess zinc in THF gives a diastereomeric mixture of 1,1′-dialkyl-3,3′-di(2-quinolyl)-1,1′,4,4′-tetrahydro-4,4′-biquinolyls. An excess of lithium in THF gives a mixture of 1′,2′-dihydro-2,3′-biquinolyl and 1′-alkyl-1′, 4′-dihydro-2,3′-biquinolyl with the former predominating. The reduction by lithium in THF of 1,1′-dialkyl-3,3′-di(2-quinolyl)-1,1′,4,4′-tetrahydro-4,4′-biquinolyls leads to analogous products. Reduction of 1-alkyl-3-(2-quinolyl)quinolinium iodides by metallic potassium gives 1-alkyl-1′,4′-dihydro-2,3′-biquinolyls.

Syntheses and Reactions of a Stable 1,2‐Dichloro‐1,2‐diborolane and Aromatic Tetraboranes

AbstractThe 1,2‐dichloro‐1,2‐diborolane 1b was isolated in good yield after the reaction of the 1,2‐bis(dimethylamino)‐1,2‐diborolane 2c with BCl3. We prepared 2c from 1,2‐bis(dimethylamino)‐1,2‐dichlorodiborane(4) (3) and TMEDA‐free [1,3‐bis(trimethylsilyl)allyl]lithium (5a·Li), which is accessible by deprotonation of 1,3‐bis(trimethylsilyl)propene (4a) with n‐butyllithium in diethyl ether. Upon its reaction with lithium in THF, the 1‐allyl‐2‐chlorodiborane(4) 6a obtained in the first step undergoes an unprecedented ring closure with 1,2‐migration of a trimethylsilyl substituent to yield the boron‐stabilized carbanion 7a. Reaction of 7a with either chlorotrimethylsilane or HCl gives 2c or 2d, respectively. The latter compound cannot be transformed into an isolable 1,2‐dichloro‐1,2‐diborolane; this observation demonstrates that a trimethylsilyl substituent next to each boron atom is essential for the stability of 1,2‐dichloro‐1,2‐diborolanes. Compound 1b is a versatile starting material, inter alia for the syntheses of the aromatic tetraboranes(6) cis‐11 and trans‐13 and the aromatic tetraborane(4) cis‐12. The isomerization cis‐11 → trans‐13 can be explained on the basis of reactions occurring under the conservation of two‐electron aromaticity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)