Methyllithium In Ether Research Articles

Transformation of 5,8-Dimethyl-1-Tetralone: Synthesis of Ar-Occidol

Reduction of 5,8-dimethyl-1-tetralone 1 with sodium borohydride in methanol followed by methylation of the resulting alcohol with methyl iodide and sodium hydride yielded a methyl ether. This was oxidised with potassium permanganate and acetonitrile to give 4-methoxy-5,8-dimethyle-1-tetralone. Methoxycarbonylation of the ketone with dimethylcarbonate (DMC) in the presence of sodium hydride in dimethoxyethane (DME) afforded β-ketoester 5 which on heating with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dioxane underwent aromatisation and elimination to furnish a naphthalene. The mesyl derivative the phenol on hydrogenation produced methyl 5,8-dimethyl-2-naphthoate. The transformation of naphthoate into ar-occidol was accomplished by a Grignard reaction with methyllithium in ether.

Synthesis and transformations of 3-acetylpyridine-2(1H)-thiones

Reactions of substituted 3-cyanopyridine-2(1H)-thiones with methyllithium gave 3-acetylpyridine-2(1H)-thiones. The best results were achieved by adding a solid-state thione to a solution of methyllithium in ether (thione: MeLi = 1: 3). The compounds obtained and their 3-pentanoyl analogs were used to synthesize a number of fused heterocyclic systems.

Bis(enamino-Cp) Group 4 metal complex chemistry: developing a Mannich-type carbon–carbon coupling reaction at the bent metallocene famework

Treatment of 6-methyl-6-dimethylaminofulvene ( 2a) with methyl lithium in ether results in a deprotonation reaction to yield the enamino-substituted lithium cyclopentadienide reagent 3a. Its reaction with zirconium tetrachloride (0.5 molar equivalents) results in the formation of the [1-dimethylaminobutadien-1,3-diyl-bis(cyclopentadienyl)]zirconium dichloride product 4a. The unsaturated ansa-metallocene is probably formed via a Lewis acid-catalyzed Mannich-type carbon–carbon coupling reaction of an in situ generated bis[(dimethylaminoethenyl)cyclopentadienyl]ZrCl 2 intermediate. A number of related examples of this condensation reaction at the intact Group 4 bent metallocene framework is described, using different amino-substituents and Ti, Zr and Hf systems. Three examples of the unsaturated ansa-metallocene systems were characterized by X-ray diffraction. In a few cases it was possible to isolate the open (enamino-Cp) 2ZrCl 2 complexes. In the case of, e.g., (piperidinoethenylcyclopentadienyl) 2ZrCl 2 ( 13c) treatment with a catalytic quantity of the Lewis acid ZrCl 4 or the Brønsted acid [ PhNMe 2 H + ] [ BPh 4 - ] resulted in a clean conversion to the respective Mannich condensation product, here the ansa-metallocene complex 4c. The strongly electrophilic borane HB(C 6F 5) 2 did not catalyze the CC-coupling reaction under the applied reaction conditions but added cleanly to the enamino-C C double bond of, e.g., 13c to yield a cyclic nitrogen donor-stabilized hydroboration product ( 19).

Selective Intramolecular [N]CH Activation in Bis(1-ethenylamino-Cp)zirconium−Butadiene Complexes and Related Systems

Treatment of 6-(dimethylamino)-6-methylpentafulvene (2a) with methyllithium in ether at −40 °C leads to CH3 addition to the C6-fulvene carbon atom to yield the [C5H4−CMe2−NMe2]Li reagent 3a, whereas treatment of 2a with MeLi in THF at −78 °C results in deprotonation with formation of [C5H4−C(CH2)−NMe2]Li (4a). In contrast, treatment of 6-diethylamino-6-methylfulvene (2b) with methyllithium under any of these conditions leads only to H+-abstraction to give [C5H4−C(CH2)−NEt2]Li (4b). Treatment of the reagents 4 with CpZrCl3 yields the enamino-Cp-substituted bent metallocenes [η5-C5H4−C(CH2)−NR2]CpZrCl2 5a (R = CH3) and 5b (R = C2H5), respectively. Analogous treatment of 4b with zirconium tetrachloride gave the doubly functionalized zirconocene complex [η5-C5H4−C(CH2)−NEt2]2ZrCl2 (6b). The complexes 5a, 5b, and 6b were characterized by X-ray diffraction. Treatment of 3a with CpZrCl3 gave [η5-C5H4−CMe2−NMe2]CpZrCl2 (8a); the analogous reaction with ZrCl4 gave [η5-C5H4−CMe2−NMe2]2ZrCl2 (8b). Both complexes 8 r...

2‐(2,4‐Di‐tert‐butylphenyl)‐1,1‐bis(trimethylsilyl)silene and 2‐(2,4,6‐Tri‐tert‐butylphenyl)‐1,1‐bis(trimethylsilyl)silene – Two New Sterically Protected but Still Unstable Silaethenes

Abstract(2,4‐Di‐tert‐butylphenyl)tris(trimethylsilyl)silylmethanol (1a), prepared by the reaction of tris(trimethylsilyl)silylmagnesium bromide with 2,4‐di‐tert‐butylbenzaldehyde, was deproto‐nated by treatment with methyllithium in ether at –78°C to give the transient 2‐(2,4‐di‐tert‐butylphenyl)‐1,1‐bis(trimeth‐ylsilyl)silene (3a), which dimerizes in a head‐to‐head fashion with the formation of (E)‐/(Z)‐3,4‐bis(2,4‐di‐tert‐butylphenyl)‐1,1,2,2‐tetrakis(trimethylsilyl)‐1,2‐disilacyclobutane (5). Besides 5 an unstable compound 4 was obtained, which was preliminarly assigned as 5,7‐di‐tert‐butyl‐1‐(2,4‐di‐tert‐bu‐tylphenyl) ‐1,2,3,8a‐tetrahydro‐2,2,3,3‐tetrakis(trimeth‐ylsilyl)‐1,2‐disilanaphthalene (4), the formal [2 + 4] cyclodimer of 3a. Compound 4 gradually decomposes to give (E)‐/(Z)‐5, and is considered to be the kinetically preferred dimer of 3a, which is converted into the thermodynamically stable 5. 2,4,6‐Tri‐tert‐butylbenzaldehyde reacts with tris(tri‐methylsilyl)silyllithium resulting in the formation of 6,8‐di‐tert‐butyl‐1,2,3,4‐tetrahydro‐4,4‐dimethyl‐2,2‐ bis(trimethylsilyl)‐2‐silanaphthalene (6). Compound 6 is the product of the insertion of the Si=C bond into the C–H bond of an o‐tert‐butyl group of the intermediate 2‐(2,4,6‐tri‐tert‐butylphenyl)‐1,1‐bis(trimethylsilyl)silene (3b), which despite extreme steric shielding proved to be still unstable. For compounds (Z)‐5 and 6 the results of the X‐ray analyses are given.

ChemInform Abstract: Reaction of Pentachloropyridine with α‐Lithiated Arylacetonitriles and Methyllithium in Ether.

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A direct and a formal trapping of propa-1,2-dienylidene

1,2-Dibromocyclopropene ring-opens in solution at 0 – 20 °C to give 1,2-dibromoprop-2-en-1-ylidene, which is trapped by alkenes; the derived cyclopropanes react efficiently with methyl lithium to produce eth-1-en-1-ylidenecyclopropanes. Reaction of the cyclopropene with methyl lithium in ether in the presence of an alkene leads to the same allenes by trapping of the parent allenic carbene, propa-1,2-dienylidene, albeit in low yield

Synthesis of Transient Silenes by a Modified Peterson Reaction

AbstractTris(trimethylsilyl)silylmagnesium bromide, obtained in situ from tris(trimethylsilyl)silyllithium and magnesium bromide, reacts with acetone, pivalaldehyde, or 2,4,6‐trimethylbenzaldehyde to give the (1‐hydroxyalkyl)tris(trimethylsilyl)silanes (Me3Si)3SiC(OH)Me2 (1a), (Me3Si)3CH(OH)tBu (1b), and (Me3Si)3SiC(OH)Mes (1c), resp. After deprotonation with methyllithium in ether at ‐78°C 1a‐c eliminate trimethylsilanolate according to a modified Peterson mechanism to form transient silenes (Me3Si)2Si=CR1R2 (6a: R1 = R2 = Me; 6b: R1 = H, R2 = tBu; 6c: R1 = H, R2 = Mes). In the absence of trapping agents these silenes dimerize, 6a leading to the linear dimer 1‐isopropenyl‐2‐isopropyl‐1,1,2,2‐tetrakis(trimethylsilyl)disilane (7) and 6b giving the head‐to‐head cyclodimerization product (E)‐3,4‐di‐tert‐butyl‐1,1,2,2‐tetrakis(trimethylsilyl)‐1,2‐disilacyclobutane (8), whereas 6c in a very unusual cyclodimerization step affords (E)‐1,2,3,8a‐tetrahydro‐1‐mesityl‐5,7,8a‐trimethyl‐2,2,3,3‐tetrakis(trimethylsilyl)‐2,3‐disilanaphthalene (9). Compound 9 is the result of an unexpected [2 + 4] reaction, in which the silene formally acts as the monoene and – involving the aromatic substituent – simultaneously also as the diene. The reaction of 1a‐c with methyllithium in THF at low temperature initiates 1,3‐Si,O‐trimethylsilyl migrations leading to (trimethylsiloxy)‐[bis(trimethylsilyl)silyl]alkanes (Me3Si)2SiH–CR1R2OSiMe3 3a‐c. Reaction of 1a‐c with an excess of methyllithium, tert‐butyllithium, or phenyllithium, leads to trisilanes (Me3Si)2‐SiR3–CHR1R2 11a‐e, formed by the addition of the organolithium reagent to the Si=C bond of the transient silences 6a‐c. Deprotonation of 1b and 1c in the presence of 2,3‐dimethyl‐1,3‐butadiene gives the [2 + 4] cycloadducts 6‐tert‐butyl‐3,4‐dimethyl‐1,1‐bis(trimethylsilyl)‐1‐sila‐3‐cyclohexene (12a) and 6‐mesityl‐3,4‐dimethyl‐1,1‐bis(trimethylsilyl)‐l‐sila‐3‐cyclohexene (12b). For 8 and 9 the results of the X‐ray analyses are given.

Reaction of Pentachloropyridine with a-Lithiated Arylacetonitriles and Methyllithium in Ether

Reaction of Pentachloropyridine with a-Lithiated Arylacetonitriles and Methyllithium in Ether

Reaction of Pentafluoropyridine and a-Lithiated Arylacetonitriles with n-Butyllithium and Methyllithium in Ether

Reaction of Pentafluoropyridine and a-Lithiated Arylacetonitriles with n-Butyllithium and Methyllithium in Ether

Asymmetric diarsines: Synthesis of dimeric pentamethylcyclopentadienylchloroarsine, dimeric pentamethylcyclopentadienyl(methyl)arsine and the crystal structure of dimeric pentamethylcyclopentadienyl(methyl)arsine

Reduction of pentamethylcyclopentadienyldichloroarsine ( 1) with cobaltocene in n-hexane affords dimeric pentamethylcyclopentadienylchloroarsine ( 2). The reaction of ( 2) with methyl lithium in ether gives dimeric pentamethylcyclopentadienyl (methyl)arsine ( 3), whose crystal structure has been determined. The crystal structure of ( 3) (triclinic, space group P 1 , a = 7.345(1), b = 8.594(1), c = 10.673(1) Å, α = 101.07(1)°, β = 104.56(1)°, γ = 113.69(1)°, Z = 1) shows two planes, one determined by two carbon atoms of the pentamethylcyclopentadienyl ligands and the two arsenic atoms, the other from two carbon atoms of the methyl ligands and the two arsenic atoms: these two planes display an angle of 78° alongside the axis formed by the two arsenic atoms. Compounds 2 and 3 are — to the best of our knowledge — the first examples of asymmetric diarsines which combine two asymmetric arsenic centres.

The synthesis of norbornanes with functionalized carbon substituents at a bridgehead. 1-(3-Oxonorborn-1-yl)ethanone and 1-(3-oxonorborn-1-yl)-2-propanone

Treatment of 2-norobornene-1-carboxylic acid (7) with one equivalent of methyllithium in ether followed by a second molar equivalent after dilution with tetrahydrofuran gave 1-(norborn-2-en-lyl)ethanone (10) and only a trace of the tertiary alcohol 11. Reaction of 7 with formic acid followed by hydrolysis gave a 4:3 mixture of exo-3- and exo-2-hydroxynorbornane-1-carboxylic acid (16 and 17), whereas oxymercuration–demercuration gave only the exo-3-hydroxy isomer 16. Oxidation of 16 and 17 gave 3- and 2-oxonorbornane-1-carboxylic acid (27 and 29), respectively. Oxymercuration–demercuration of 10 gave exclusively 1-(exo-3-hydroxynorborn-1-yl)ethanone (30), which was also prepared by treatment of 16 with methyllithium in analogous fashion to that used for the conversion of 7 to 10. Oxidation of 30 gave 1-(3-oxonorborn-1-yl)ethanone (1). Dehydrobromination of exo-2-bromonorbornane-1-acetic acid and dehydration of 2-hydroxy-norbornane-2-acetic acid derivatives gave 1-(norborn-2-ylidene) acetic acid derivatives to the exclusion of norborn-2-ene-1 -acetic acid derivatives. Treatment of exo-5-acetyloxy-2-norobornanone (52) with ethyl bromoacetate and zinc gave ethyl exo-5-acetyloxy-2-hydroxynorbornane-(exo- and endo-2-acetate (53 and 54). Reaction of 53 with hydrogen bromide gave initially ethyl endo-3-acetyloxy-exo-6-bromonorbornane-1-acetate (59), which was subsequently converted to a mixture of 59 and its exo-3-acetyloxy epimer 61. Catalytic hydrogenation of this mixture gave a mixture of ethyl endo- and exo-3-acetyloxynorbornane-1 -acetate (62 and 63). Basic hydrolysis of this gave a mixture of the corresponding hydroxy acids, 70 and 71; the former was slowly converted to the latter at pH 5. Oxidation of the mixture of 70 and 71 gave 3-oxonorbornane-1-acetic acid (72). Treatment of the mixture with methyllithium as for 16 gave a mixture of 1-(endo- and exo-3-hydroxynorborn-1-yl)-2-propanone (73 and 74), which was oxidized to 1-(3-oxo-norborn-1-yl)-2-propanone (2). Reaction of exo-2-hydroxynorbornane-1-acetic acid lactone (75) with methyllithium in ether gave (1-(exo-2-hydroxynorborn-1-yl)-2-propanone (76), which on oxidation gave the 2-oxo isomer 78 of 2.

Concerning the Synthesis of [1.1.1]Propellane

AbstractThe reaction of 1,1‐dibromo‐2,2‐bis(chloromethyl)cyclopropane (2) with methyllithium in ether led to a solution of [1.1.1]‐propellane (1) in a yield of 70%. 1 could also be prepared free of solvent by reaction of 2 with lithium powder in triglyme/n‐decane at 73°C.

The preparation and lithiation of 1-halogenocyclopropenes

Reaction of a range of 1,1,2-trihalogenocyclopropanes (halogen = bromine, chlorine) with methyl-lithium in ether at –90–20 °C leads to 1,2-dehalogenation to the corresponding 1-halogenocyclopropene. The halogenocyclopropenes are readily lithiated by lithium–halogen exchange with a second equivalent of methyl-lithium to give 1-lithiocyclopropenes, which are in turn trapped by electrophiles; an exception to this is compound (21; X = Cl), which leads to 3-methylbuta-1,2-dienylidene (31) by initial lithium–hydrogen exchange and loss of lithium chloride. The cyclopropenes (5; R = Me, X = Br or Cl) and (21; X = Br or Cl) decompose even at temperatures around ambient, leading either to enynes (6; R = Me) or halogenoalkynes (18; X = Br or Cl). A 12C-labelling study indicates that C-1 of the cyclopropene (21; X = Cl) becomes C-2 of the alkyne (18; X = Cl) on rearrangement.

A simple route to 1-bromobicyclo[1.1.0]butanes by intramolecular trapping of 1-bromo-1-lithiocyclopropanes

Reaction of the dibromides (5) and (10) with methyl lithium in ether leads to products derived by 1,3-dehalogenation, (6) and (11), whereas (15) and (16) undergo 1,1-dehalogenation and rearrangement to allenes, (17) and (18).

Cyclopropene-carbene rearrangements at low temperatures. Generation and trapping of 1,2-dichloro-3-methylbut-2-en-1-ylidene

Reaction of (5, X = H, Cl, Br) with methyl lithium in ether in the presence alkenes leads to cyclopropanes, e g.(6), apparently derived by trapping of an intermediate carbene (4); in the case of (5, X = Br), the precursor of the carbene, a cyclopropene (1, X=Y=Cl, Z=Me), may be trapped by addition of bromine at −90°C.

1,1-Dihalogenocyclopropanes derived from terpenes. The stereochemistry of cyclopropylidene insertion into carbon–hydrogen bonds adjacent to alcohols

Treatment of the alcohol (13) with methyl-lithium in ether leads to the ketone (5), whereas (12) gives no ketone and the major product is the alcohol (16). The formation of (5) from (13) establishes the requirement for a syn-relationship between a C–H bond at the 1-position and C-2′ in the conversion of 1-(2′,2′-dibromocyclopropyl)alkan-1-ols into (cyclopropyl)alkyl ketones.

Five-membered ring spiro-annulation via thermal rearrangement of enol silyl ethers of 2-(cyclopropylmethylene)cycloalkanones. A formal total synthesis of some spirovetivane-type sesquiterpenoids

Treatment of the 2-(iodomethylene)cycloalkanones 10 and 11 with lithium (phenylthio)(cyclopropyl)cuprate provided good yields of the corresponding β-cyclopropyl enones 12 and 13, respectively. Thermolysis of the latter substances produced relatively poor yields of the desired spiro-annulation products 14 and 15. However, conversion of 12 and 13 into the corresponding enol silyl ethers 24 and 25, followed by thermal rearrangement of the latter materials and acid hydrolysis of the resulting products, provided synthetically useful yields of the spiro enones 14 and 15. Cuprous iodide-catalyzed addition of methyl magnesium iodide to 2-cyclohexen-1-one, followed by trapping of the resultant enolate anion with cyclopropanecarboxaldehyde, provided the ketols 38, which could be converted readily into the mixture of enol silyl ethers 34 and 35. Thermal rearrangement of the latter substances gave, after acid hydrolysis of the crude thermolysate, the spiro enones 42 and 43 in a ratio of ~2.5:1 (57% yield). Treatment of 42 with methyllithium in ether gave the tertiary alcohols 44 and 45 (ratio ~4:1). Hydroboration (disiamylborane, tetrahydrofuran; H2O2, NaOH) of 44, followed by oxidation of the resultant diol 46 with pyridinium chlorochromate, provided the ketol 47. A similar sequence of reactions converted the olefinic alcohol 45 into the ketol 49. Dehydration (p-toluenesulfonic acid in benzene) of 47 gave the spiro enones 28 and 48, in a ratio of ~9:1. Compound 28, also prepared previously from the ketol 49, had been converted earlier into the spirovetivane-type sesquiterpenoids (±)-α-vetispirene (29), (±)-β-vetivone (30), (±)-hinesol (31), (±)-hinesol acetate (32), and (±)-agarospirol (33).

ChemInform Abstract: CYCLOPROPYLIDENE INSERTION REACTIONS: 2‐METHOXY‐1,2‐DIMETHYLBICYCLO(1.1.0)BUTANE

AbstractIm Rahmen von Studien zur Synthese von Bicyclo[l.1.0]butanen mit O‐Funktion am Brückenkopf‐C‐Atom werden die Umwandlungen der Dibrom‐ bzw. Dichlorcyclopropane (II) und (III) unter der Einwirkung von Methyl‐Li untersucht.

Notizen: Bis(trimethylstannyl)lithiumphosphid / Bis(trimethylstannyl)lithiumphosphide

Tris(trimethylstannyl)phosphine reacts with methyllithium in ether forming tetramethyltin and bis (trimethylstannyl)lithiumphosphidemonoetherate in high yields. The Raman, ¹H and ³¹P NMR spectra are reported and discussed. The compound does not form a stannylated diphosphine with 1,2-dibromoethane.