WO2000041987A1

WO2000041987A1 - Method for producing substituted cyclopentadienes

Info

Publication number: WO2000041987A1
Application number: PCT/EP2000/000015
Authority: WO
Inventors: Carsten Bingel
Original assignee: Basell Polypropylen Gmbh
Priority date: 1999-01-12
Filing date: 2000-01-04
Publication date: 2000-07-20

Abstract

The invention relates to a method for producing substituted cyclopentadienes, especially 1,3-disubstituted, cyclopentadienes which are produced from substituted cyclopent-2-en-1-ones.

Description

Process for the preparation of substituted cyclopentadienes

description

The present invention relates to a process for the preparation of substituted, in particular 1,3-disubstituted, cyclopentadienes, which are prepared starting from substituted-cyclopent-2-en-1-ones.

Alkyl and aryl-substituted cyclopentadienes are used for the production of metallocene complexes ("Chemistry of Organozirconium and - hafnium compounds -", DJ Cardin, MF Läppert, CL Raston; 1986, Ellis Horwood Limited) such as, for example, metallocenes of titanium, zirconium, hafnium or lanthanoids used. These metallocenes are part of highly active catalyst systems for the production of polyolefins, in particular polyethylenes and copolymers of ethylene with other α-olefins (WO9504761).

The synthesis of substituted, in particular 1, 3-disubstituted cyclopentadienes starting from substituted, in particular from 3-substituted cyclopent-2-en-1-ones is generally described in the literature (EP-A-0729967; EP- A-0648722; Chem. Ber. 109, 329-336 (1976); Tetrahedron (1965), 21, 2313) and follows scheme (1):

R, R ^{1 are} identical or different alkyl or aryl radicals and M is Li, MgCl, MgBr or Mgl.

A tertiary alcoholate is formed by the reaction with a Grignard compound or organolithium compound. After protonation and acid-catalyzed dehydration, 1,3-disubstituted cyclopentadiene is formed. The reaction proceeding according to scheme (1) takes place without problems in the manner shown if R ^{1 is,} for example, an aryl radical or tertiary butyl radical. From EP-A-0648722 it is known that when alkyl grigards such as

Methyl, ethyl propyl or isopropyl magnesium halide, after alcohol formation and acid-catalyzed dehydration, in addition to the desired endo isomers (cyclopentadienes), undesirable exo isomers are also formed. This is described in the following scheme (2):

where M is Li, MgCl, MgBr or Mgl and

R, R ² , R ^{3 may be the} same or different alkyl or aryl radicals.

If - as described in EP-A-0648722 - a strong acid is used to dehydrate the tertiary alcohol, an endo / exo isomer ratio of about 1: 1 is obtained. Furthermore, EP-A-0648722 describes that at Using carboxylic acids in dehydration the ratio of endo / exo can be improved to 2.5: 1.

A disadvantage of the process described in EP-A-0648722 is that the conversion to the alcoholate is first carried out in diethyl ether / THF, and that the alcoholate is then added to an aqueous carboxylic acid solution. For safety reasons, the solvent diethyl ether should not be used on an industrial scale. Furthermore, the use of two reactors, one for the alcoholate synthesis and one for the dehydration, is expensive.

The object was therefore to find a process for the preparation of substituted, in particular 1,3-disubstituted, cyclopentanes which avoids the disadvantages mentioned above and can be carried out without problems under technical conditions.

It has now surprisingly been found that the disadvantages described above from a technical point of view, despite the use of strong mineral acids for dehydration, by means of a suitable reaction can be avoided without worsening the endo / exo selectivity.

The present invention thus relates to a process for the preparation of substituted, in particular 1,3-disubstituted, cyclopentadienes comprising the steps:

a) reaction of a compound of formula (I)

with a compound of formula (II)

R ² R ³ CH-M (II)

wherein

R is a -C-C ₀ hydrocarbon radical, preferably equal to alkyl or aryl and particularly preferably equal to methyl or phenyl, and

R ² , R ^{3 are the} same or different hydrogen or a -C ~ C ₂ o hydrocarbon radical, preferably hydrogen, alkyl or aryl, particularly preferably hydrogen or a linear or branched Ci-Cβ alkyl radical, and

R ⁴ , R ⁵ , R ^{6 are} identical or different hydrogen or a -C ₂₀ hydrocarbon radical, preferably hydrogen, alkyl or aryl, particularly preferably hydrogen, and

M is Li, MgCl, MgBr or Mgl

in one or more inert organic solvents to a compound of formula (III)

b) optionally separating the inert organic solvent from step a) and adding one or more water-immiscible organic solvents

c) adding a strong, aqueous inorganic acid in order to achieve protonation and dehydration of the compound of the formula (III) formed in step a) to form the compounds of the formula (IVa) and (IVb).

d) separating the acidic aqueous phase and working up the organic phase containing the compounds of the formula (IVa) and (IVb).

In the process according to the invention, a substituted, in particular a 3-position-substituted-cyclopent-2-en-l-one is first reacted with a Grignard compound or an organolithium compound MCHR ² R ³ to give the tertiary alcoholate. The alcoholate is then dehydrated in the same reactor by adding a strong inorganic acid in an aqueous two-phase system to an endo / exo isomer mixture, the desired endo content being at least 70% (based on the total amount of endo / exo).

The organic solvent phase must be practically immiscible with the aqueous acid phase in order to avoid acid-catalyzed isomerization from the endo isomer to the exo isomer. The presence of acidic compounds that are soluble in both the aqueous and organic phases should also be avoided. If the organic phase contains large proportions of a water-miscible solvent, the endo / exo ratio deteriorates. This problem could be solved by a partial change of solvent, for example by a water-miscible solvent such as tetrahydrofuran is partially distilled off, by a hydrocarbon such as an alkane or an aromatic or corresponding mixtures, such as pentane, hexane, isohexane, heptane, ^® Exxsol DSP 100-120, toluene, Xylene, ethylbenzene, tetrahydronaphthalene, preferably heptane, is replaced and only then is the aqueous mineral acid added. The reaction proceeds as follows:

The strong, aqueous inorganic acids used are preferably those whose pKa value is less than 4. In particular hydrochloric acid, sulfuric acid or phosphoric acid is used.

The substituted-2-cyclopentene-l-ones are known in part from the literature. The preferred 3-substituted-2-cyclopenten-1-ones can be prepared from 1, -diketones, for example, by methods known from the literature (J. Chem. Soc. 1127 (1952); US Pat. No. 5,026,919; J. Org. Chem. 55: 311-315 (1990); Tetrahedron 39: 4127-4132 (1983)). 3-Methyl- or 3-phenyl-2-cyclopenten-l-ones are preferred.

The organometallic compounds R ² R ³ CHM, where R ² , R ³ and M are as defined above, are commercially available or can be easily prepared by processes known from the literature (for example Grignard compounds: Organikum, 15th edition, VEB German Publishing House of Sciences, Berlin 1981, p. 623).

The reaction of the organometallic compound with the cyclopent-2-en-1-one can be in a ratio of 1: 1 to 1.5: 1, preferably 1.1 to 1.3: 1 in ether-containing solvents or solvent mixtures which are an ether but not diethyl ether , and contain a hydrocarbon, preferably tetrahydrofuran as ether and heptane or toluene as hydrocarbon, in a temperature range from -78 ° C to 110 ° C, preferably -10 ° C to 50 ° C.

After the two reaction components have been combined, the mixture is stirred for a further 0 to 5 h, preferably 1 to 3 h at a temperature of 0 ° C. to 110 ° C., preferably 20 ° C. to 50 ° C., before under reduced pressure, 800 mbar to 100 mbar, preferably 400 to 600 mbar, the ether, in particular tetrahydrofuran, is largely distilled off. The distilled-off water-miscible solvent or the solvent component is replaced by a water-immiscible hydrocarbon, as described above, preferably n-heptane.

Mineral acid, preferably hydrochloric acid, sulfuric acid or phosphoric acid, particularly preferably dilute sulfuric acid, is added to the suspension of the alcoholate in the hydrocarbon at a temperature of -30 ° C. to 50 ° C., preferably -5 ° C. to 10 ° C., with vigorous stirring added dropwise, the volume of the aqueous acid phase to the volume of the organic phase being 2: 1 to 0.5: 1. The molar ratio of the protons to the organometallic compound used is 1: 1 to 4: 1, preferably 1.5: 1 to 2.5: 1. After the complete addition of acid, the pH of the aqueous phase is less than 4, preferably less than 2.

After the acid has been added, stirring is continued for up to 30 min until the dehydration of the tertiary alcohol has been completed.

The entire reaction procedure is characterized in that the various reaction steps, the possible production of an organometallic compound, for example the production of a Grignard compound, the reaction of the substituted cyclopent-2-en-l-one with the organometallic compound, the subsequent protonation of the tertiary alcoholate and the acid-catalyzed dehydration of the tertiary alcohol to the substituted cyclopentadiene, all of which are carried out in succession in the same reaction vessel.

In addition to the desired endo isomer, the cyclopentadiene derivative, the dehydration also produces the undesired exo isomer, the ratio endo / exo> 1.5: 1, preferably> 2: 1.

The endo / exo isomer mixture can be obtained by distillation under reduced pressure. The content of the endo isomer can be determined by gas chromatography in order to calculate the amount of base required for deprotonating the substituted cyclopentadiene, such as, for example, butyllithium, methyllithium, phenyllithium, dibutylmagnesium, butylmagnesium chloride, sodium hydride or potassium hydride. The substituted cyclopentadienyl alkali metal or alkaline earth metal salt prepared in this way can be prepared by known methods by reaction with the halides of titanium, zirconium, hafnium or the lanthanoids, preferably zirconium tetrachloride or the ether complexes of ZrCl ₄ , for example ZrCl ₄ * 2THF or ZrCl * DME, to be converted to the corresponding metallocene.

The invention is illustrated by the following examples, which, however, are not intended to restrict the invention. Example la)

Preparation of 1, 3-n-butyl-methyl-cyclopentadiene

A solution of 9.9 ml (100 mmol) of 3-methyl-2-cyclopent-2-en-l-one in 16 ml of toluene / 4 was added to 41 ml (110 mmol) of a solution of butyllithium in toluene (2.68 molar) ml of THF added dropwise at -10 ° C to 30 ° C. The mixture was stirred at 30 ° C for 1 hour. 30 ml of toluene were then added. At 0 ° C to 5 ° C, 10 g of water and then 36 ml of 2 molar sulfuric acid were added dropwise with vigorous stirring. After 0.5 h the phases were separated, the organic phase was washed with 20 ml of 2 molar sulfuric acid, 40 ml of saturated sodium bicarbonate and 40 ml of saturated saline and dried with 5 g of magnesium sulfate. The GC of the crude product shows an endo / exo ratio of 2.4: 1.

Example lb)

Preparation of 1, 3-n-butyl-methyl-cyclopentadiene

The preparation of n-butylmagnesium chloride and the subsequent addition to 3-methyl-2-cyclopent-2-en-l-one was carried out in a dry apparatus flushed with protective gas under protective gas.

34.6 g (1.42 mol) of magnesium were placed in 60 ml of THF and 1.0 ml of dibromoethane was added. 115.5 g (1.25 mol) of 1-chloro-butane were added dropwise as a solution in 250 ml of THF to the magnesium shavings, the rate of addition being adjusted so that the reaction mixture boiled gently under reflux. After the addition had ended, the Grignard solution was stirred at 75 ° C. for a further 2 h. The Grignard solution was cooled to 0 ° C. and a solution of 104.3 g (1.06 mol) of 3-methyl-2-cyclopent-2-en-l-one in 60 ml of THF and 205 ml of n-heptane was added dropwise so that the internal temperature Do not exceed 30 ° C. The suspension was then stirred at 30 ° C. for 2 h. At 500 mbar, most of the THF was distilled off together with heptane (bath temperature: 70 ° C; head temperature: 41 ° C; 260 ml solvent). Then 380 ml of n-heptane were added to the slurry-like suspension and the contents of the flask were cooled to 0 ° C. in a common salt-ice mixture. A total of 620 ml of 2 molar sulfuric acid were slowly metered in with stirring so that the temperature did not exceed 5 ° C. After finished Acid addition was stirred for a further 10 minutes. The viscous two-phase mixture was separated in a separating funnel and the aqueous acid phase was extracted twice with a total of 260 ml of n-heptane. The combined organic phases were washed with 150 ml of sodium hydrogen carbonate solution (saturated) and with 150 ml of sodium chloride solution (saturated) and dried with 40 g of magnesium sulfate (30 minutes). After removing the solvent on a rotary evaporator (bath: 40 ° C; 50 mbar), 173 g of crude product were obtained. The crude product was distilled in an oil pump vacuum over a 30 cm Vigreux column with a column top (bath: 83-102 ° C; top: 52-48 ° C; 8.5-7.2 mbar). 100.4 g of a slightly yellowish liquid were obtained which, according to GC, contained the desired 1,3-butyl-methyl-cyclopentadiene isomers to the exo isomers in a ratio of 2.8: 1.

Comparative Example 2a)

Preparation of 1, 3-n-butyl-methyl-cyclopentadiene in the presence of HNEt ₃ Cl

A solution of 9.9 ml (100 mmol) of 3-methyl-2-cyclopent-2-en-l-one in 20 ml of heptane / 6 ml of THF at 20 ° C. was added to 42 ml (120 mmol) of a solution of butyl magnesium chloride in THF added dropwise up to 40 ° C. The mixture was stirred at 30 ° C for 1 hour. Then 29 ml of heptane were added. At 0 ° C. to 5 ° C., 3 g of water, 1.4 ml (10 mmol) of triethylamine and then 31 ml of 2 molar sulfuric acid were added dropwise with vigorous stirring. After 0.2 h, the phases were separated, the organic phase was washed with 40 ml of saturated sodium hydrogen carbonate and 40 ml of saturated sodium chloride solution and dried with 5 g of magnesium sulfate. The GC of the crude product shows an endo / exo ratio of 0.9: 1.

Comparative Example 2b)

Preparation of 1, 3-n-butyl-methyl-cyclopentadiene in THF / hexane 1.8: 1

3.16 g (0.13 mol) of magnesium were placed in 6.5 ml of THF and 0.2 ml of dibromoethane was added. 10.2 g (0.11 mol) of 1-chloro-butane were added dropwise to the magnesium shavings as a solution in 25 ml of THF, the dropwise rate being adjusted so that the reaction mixture boiled gently at reflux. After the addition had ended, the Grignard solution was heated under reflux for a further 2 h. The Grignard solution was cooled to 0 ° C. and a solution of 9 ml (100 mmol) of 3-methyl-2-cyclopent-2-en-1-one in 20 ml of heptane / 6 ml of THF was added dropwise. The mixture was stirred at 30 ° C for 1 hour. At 0 ° C to 25 ° C, 10 g of water and then 40 ml of 2 molar sulfur acid added dropwise with vigorous stirring. After 0.1 h the phases were separated, the organic phase was washed with 40 ml of water and dried with 5 g of magnesium sulfate. The GC of the crude product shows an endo / exo ratio of 1: 1.

Comparative Example 2c)

Preparation of 1, 3-n-butyl-methyl-cyclopentadiene in THF / toluene 1: 1.6

3.16 g (0.13 mol) of magnesium were placed in 6.5 ml of THF and 0.2 ml of dibromoethane was added. 11.1 g (0.12 mol) of 1-chloro-butane were added dropwise to the magnesium shavings as a solution in 25 ml of THF, the dropping rate being adjusted so that the reaction mixture boiled gently at reflux. After the addition had ended, the Grignard solution was heated under reflux for a further 2 h. The Grignard solution was cooled to -10 ° C. and a solution of 9.9 ml (100 mmol) of 3-methyl-2-cyclopent-2-en-l-one in 20 ml of toluene was added dropwise. The mixture was stirred at 24 ° C for 2 hours. 30 ml of toluene were added. At 0 ° C to 25 ° C, 3 g of water and then 60 ml of 2 molar sulfuric acid were added dropwise with vigorous stirring, the temperature rising to 40 ° C. The mixture was then stirred at 60 ° C for 1 h. The phases were separated, the organic phase was washed with 40 ml of water and dried with 5 g of magnesium sulfate. The GC of the crude product shows an endo / exo ratio of 1: 1.4.

Claims

claims

1. A process for the preparation of substituted cyclopentadienes comprising the steps:

a) reaction of a compound of formula (I)

with a compound of formula (II)

R ² R ³ CH-M (II)

wherein

R is a C ₁ -C ₂₀ hydrocarbon radical, and

R ² , R ^{3 are} identical or different hydrogen or a Cχ-C ₂ o hydrocarbon radical, preferably hydrogen, alkyl or aryl, particularly preferably hydrogen or a linear or branched Cι-C ₈ alkyl radical, and

R ⁴ , R ⁵ , R ^{6 are} identical or different hydrogen or a -C ~ C o hydrocarbon radical, preferably hydrogen, alkyl or aryl, particularly preferably hydrogen, and

M is Li, MgCl, MgBr or Mgl

in one or more inert organic solvents to a compound of formula (III)

2. The method according to claim 1, characterized in that an acid with a pKs value less than 4 is used as the strong, aqueous inorganic acid.

A method according to claim 2, characterized in that hydrochloric acid, sulfuric acid or phosphoric acid is used.

Method according to one of claims 1 to 3, characterized in that one or more inert water-immiscible organic solvents are used in step a) and step b) can be omitted.