FR2499070A1 - PROCESS FOR THE PREPARATION OF 2,2-DIMETHYL-3- (B-FLUORO-B-TRIFLUOROMETHYL-VINYL) -CYCLOPROPANECARBOXYLIC ACID AND USE THEREOF AS INTERMEDIATE FOR THE PREPARATION OF PYRETHROIDS - Google Patents

Abstract

THE SUBJECT OF THE PRESENT INVENTION IS A PROCESS FOR PREPARING 2,2-DIMETHYL-3- (B-FLUORO-B-TRIFLUOROMETHYL-VINYL) -CYCLOPROPANECARBOXYL ACID. THESE COMPOUNDS ARE PREPARED BY REACTION OF A HALOGENIDE OF 2,4-DI-HALO-4,5,5,5-TETRAFLUORO-PENTANOIC ACID, WITH ISOBUTENE, IN THE PRESENCE OF A BASE AND A SOLVENT INERT, THEN HEATING THE RESULTING 2-HALO-CYCLOBUTANONE (III), IN AN INERT SOLVENT AND IN THE PRESENCE OF A QUATERNARY AMMONIUM SALT OR A TERTIARY ALIPHATIC AMINE AND REARRANGEMENT OF THE RESULTING 4-HALOCYCLOBUTANONE (IV), THAT L 'TREAT WITH ALKALINE BASES IN AN INERT SOLVENT. THE INVENTION RELATES TO THE USE OF THESE COMPOUNDS AS INTERMEDIARIES IN THE PREPARATION OF PYRETHROIDS.

Description

I 2499070

  PROCESS FOR THE PREPARATION OF 2,2-DIMETHYL-3- (e-FLUORO) ACID

  e-trifluoromethyl-vinyl) -cyclopropanecarboxylic acid,

  AND ITS USE AS AN INTERMEDIATE FOR THE PREPARATION OF PYRETHROIDS.

  The present invention relates to a method for obtaining information

  intermediates for the preparation of pyrethroids and relates more particularly

  to a process for the preparation of 2,2-dimethyl-3-fluorophosphoric acid

  O-trifluoromethylvinyl) cyclopropanecarboxylic acid and at the new

  mediates obtained from them in the various steps of the process.

  2,2-Dimethyl-3 - (--fluoro-e-trifluoromethyl-vinyl) -cycloacetate

  propanecarboxylic acid (hereinafter referred to as "compound I") of the formula:

H3C CH3

CF3 C

C = CH - CH CH - COOH (I)

  is an intermediate of the preparation of pyrethroid insecticides with high pesticidal activity, said insecticides of the type

  Pyréthrolde being described in Italian Patent Application No. 20,713 A / 78.

  For the preparation of said pyrethrins, compound I is converted to the corresponding acyl chloride which is then condensed with the appropriate alcohols such as, for example, 3-phenoxy-benzyl alcohol, alcohol, and the like.

  α-cyano-3-phenoxybenzyl or 2-methyl-5-benzyl-3-furylmethyl alcohol.

  The level of pesticidal activity developed by these pyrethroids depends on

  the isomer state of the cyclopropane ring.

  In fact, the trans isomer, though being similarly talented. a good insecticidal activity, has an insecticidal activity lower than that of the cis isomer. In the Italian patent applications Nos. 714 A / 78 and 31,310 A / 78 are described two processes for the preparation of compound I. These processes can be schematized by the described reaction sequence

  in diagrams 1 and 2 respectively.

s

SCHEME 1

  a) CF3-CFBr2 + CH2 'CH-C (CH3) 2 -CH2-COOR-

  - CF3-CFBr-CH2-CHBr-C (CH3) 2 -CH2-COOR (A)

H3C CH3

  C bases / b) A (b2HseBr) CF3-CF = CH-CH-CH-COOR (B) c) B hydrolysis (I)

(R = lower alkyl radical).

  Reaction a) consists of the addition of 1,1-dibromo-tetrafluoro-

  ethane to an ester of 3,3-dimethyl-4-pentenolic acid.

  The adduct "A" thus obtained is then treated with bases (reaction b) and undergoes two consecutive dehydrohalogenations with simultaneous closure

  cyclopropane nucleus. This reaction leads to the production of alkyl (inf) -

  esters of compound I (B) which are then subjected to hydrolysis to obtain

the free acid (reaction c).

- SCHEME 2 -

  a ') CF3 - CFBr2 + CH2 = CH - C (CH3) 2 - CH (COOR) 2 -

  CF3-CFBr-CH2-CHBr-C (CH3) 2-CH (COOR) 2 (C)

H3C CH3

  bases (b) CF3-CF CH-CH- - COOR (D) COOR c ') D hydrolysis, (I)

-C02, -ROH

(R = lower alkyl radical).

  The reaction of Scheme 2 consists of the addition of 1,1-dibromo-tetra-

  fluoroethane to a 2-alkoxycarbonyl-3,3-dimethyl-4-pentene acid ester

  nolque. The treatment of adduct "C" with bases (reaction b ') leads to the formation of 1,1-cyclopropane dicarboxylic ester (D) which, subjected to hydrolysis, under particular conditions and at a temperature

  high, leads to compound I (reaction c ').

  The processes described in Schemes 1 and 2 make it possible to obtain the compound I as an isomeric mixture on the cyclopropane ring in a

  cis / trans ratio close to the unit.

  It has been noted by the Applicant, and this forms the subject of the pre-

  invention, that compound I could be synthesized by a new

process. -

  Thus, the process forming the subject of the invention comprises, as a first step, the preparation of a halide (chloride or bromide) of 2,4-di-halo-4,5,5,5- tetrafluoro-pentanol (II), of formula:

CF3 - CF - CH2 - CH - C - Z (II)

I I I

X Y 0

  in which: X, Y and z, identical to or different from each other, represent an atom

chlorine or bromine.

  Compound II can be prepared directly by reaction of 1,1-di-

  halo-tetrafluoroethane with an acryloyl halide (reaction I, scheme 3) or by the reaction of the same perhaloethane with an acrylic ester, and then the

  subsequent conversion of the thus-obtained ester to the acyl halide cor-

  respondent (reactions 2a, 2b and 2c, diagram 3).

  According to another embodiment, the perhaloethane is reacted with the allylic alcohol, then the product thus obtained is oxidized to the carboxylic acid and finally the corresponding acyl chloride is prepared (reactions

3a, 3b and 3c, diagram 3).

  Compound II is then condensed with isobutene in order to obtain 2halo-2 - (- 2'-halo-2 ', 3', 3 ', 3'-tetrafluoropropyl) -3,3-dimethylcyclobutanone (III) which by treatment with suitable catalysts is rearranged to 2- (2'-halo-2 ', 3', 3 ', 3'-tetrafluoropropyl) -3,3-dimethyl-4halo-cyclobutanone

(IV).

  Compound (IV), by treatment with bases, leads to cyclic acid.

propanecarboxylic (I).

4 2499070

  Compared to the two aforementioned methods (diagrams 1 and 2), the method which is the subject of the invention has considerable advantages under

  the economic angle in that it starts from raw materials (derives

  acrylic acid and isobutene) at low costs and readily available.

  Nibles. The various stages of the process, moreover, are easy to put

  implemented and ensure high returns.

  Another considerable advantage of the invention lies in the fact

  that the compound of formula I is obtained in the form of a mixture of iso-

  on the cyclopropane nucleus with a higher cis / trans ratio

at 4/1.

  The reactions involved in the process according to the present invention are shown in Scheme 3 and discussed below: Scheme 3 1) CF3-CFXY + CH2 CH C-Z catalyst-CF3-CF-CH2-CH-CZ (II) II I It

0 X Y 0

  2a) CF3-CFXY + CHa, CH-C-OR CF3-CF-CH2-CH-C-OR catalysts (A)

I.I I

  o X Y O 2b) (A) CF3-CF-CH2-CH C-OH (B)

- I | I I

X Y 0

  2c) (B) HaLogent (II) agent 3a) CF3-CFXY + CH2 = CH-CHa-OH catalyst, CF3CF-CH2-CH-CH20H (C)

I I

  x Y 3b) (C) oxidation. CF3-CF-CH2-CH-COOH (B)

X Y

3c) (B) halogenating agent (II)

C \ / CH

  C 4) (II). base 4) (II) + CH2 = C (CH3) 2- b CF3-CF-CH2-C CH2 (III)

X Y C \

X y C I

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H3C CH3

  5) (III) CF3 catalyst CF-CH2 -CH CH Y (IV)

X C

I

H3C CH3

based

  6) (IV) -HX-CF 3 -CF = CH-CH-CH-COOH (I)

  -HY [X, Y and Z (same or different from each other) = Cl, Br,

  R = an alkyl radical having 1 to 4 carbon atoms.

  Reaction I of Scheme 3 consists of the addition of 1,1-dihalo

  tetrafluoroethane & acryloyl halide (either chloride or bromide)

  in order to obtain the adduct II, that is to say the halide of the 2,4dihalo acid

4,5,5,5-tétrafluoropentanolque.

  In the case where the starting perhaloethane is 1,1-dibromo-tetra-

  Fluoroethane (X = Y = Br), the reaction is suitably conducted in an autoclave and in the presence of ferpentacarbonyl and direthylformamide (DMF) in catalytic proportions. It is not necessary to use

solvents.

  Reactions 2a, 2b and 2c correspond to an embodiment which constitutes an alternative to reaction 1, insofar as they

  lead to obtaining the adduct II.

  Reaction 2a. analogous to reaction 1, is carried out using an alkyl ester instead of a halide of an acidic acrylic acid; in this case, instead of getting the acyl halide II, we get

the corresponding ester A.

  The latter is then converted into the corresponding carboxylic acid

  (B) (reaction 2b) and converted to acyl chloride II (reaction 2c).

  3b Both reactions 2b and 2c are carried out by methods which

are common in organic chemistry.

  However, it is preferable to carry out the reaction 2b by means of a transesterification in order to avoid possible dehydrohalogenations, in the case where the hydrolysis is carried out in a

basic medium.

  Reactions 3a, 3b and 3c represent another alternative to the process of reaction 1. Reaction 3a, analogous to reaction 1, consists in reacting a perhaloethane with the allyl alcohol, so as to lead to the obtaining of a pentyl polyhalogen alcohol (C). The alcohol radical of the compound "C" is then oxidized (reaction 3b) according to the techniques conventionally used in organic chemistry to yield the carboxylic acid B (identical to the compound obtained by the reaction 2b) which is then converted into the halide of corresponding acyl (reaction 3c) analogously to

that of reaction 2c.

  When the acyl halide II has been obtained according to one of the processes indicated above, it is reacted with isobutene to lead to

  obtaining cyclobutanone III, according to the reaction 4.

  Reaction 4 is carried out by reaction of an excess of isobutene with adduct II in an autoclave and in the presence of an inert solvent and a

  stoichiometric amount relative to the adduct II, a tertiary amine.

  Reaction 5 represents in its general characteristics a particular example of a known reaction, called "kinetic substitution"

  wherein a halogen atom enters at position 4 of a 2-halo-cyclohexyl

  butanone to simultaneously eliminate the halogen in position 2.

  When the reaction is carried out catalytically and the group entering position 4 is the same halogen that left

  position 2, the reaction is of the type of "kinetic rearrangement".

  The reaction described above can be carried out with the aid of a

  tertiary amine or quaternary ammonium salt catalyst or by heating 2-halo-cyclobutanone in polar aprotic solvents. Reaction 6 is carried out by simple treatment of compound IV by

  bases in inert solvents.

  The reactions mentioned above, which form the process making

  object of the invention can be carried out according to operative variants

different places.

  A practical embodiment of the method, which summarizes the indications resulting from the study of the various phases or steps of the process is described

  below and is further illustrated by operative examples.

  Reactions 1 and 2a (Scheme 3) can conveniently be carried out by introduction into an autoclave of 2 to 3 moles of CF3-CFXY and a catalytic amount of dimethylformamide (DMF) equal for example

at 4% by weight.

  At a temperature of about 140 ° C., one mole of CF3-CFXY is introduced into the autoclave, separately and little by little, in which about 1% by weight of iron pentacarbonyl and one mole of the derivative of the acid

  acrylic (respectively chloride or ester).

  The mixture is then stirred for 3 to 7 hours at the same temperature, after which the compound II or "A" is distilled off.

  respectively, in high yield (85 to 90% with respect to the acrylic derivative

employee).

  Reaction 3a can also suitably be carried out in the presence of an iron pentacarbonyl catalyst used either

  as such, or in solution in an alcohol solvent.

  The reaction 2b is obtained with good results thanks to a trans-

  esterification, for example, with formic acid in the presence of a small amount of a mineral acid, according to the usual techniques

used in organic chemistry.

  The oxidation of alcohol C to carboxylic acid "B" (reaction 3b) is carried out easily using a conventional oxidation system used in this type of reaction, such as, for example, nitric acid.

  concentrated in the presence of copper salts and vanadium pentoxide (V205).

  Similarly, the reaction 2c (and 3c) consisting of the conversion of the carboxylic acid "B" to the corresponding acid halide is carried out using standard techniques. A suitable halogenating agent is thionyl chloride, which results in the compounds of formula

(II), wherein z = CL.

  Reaction 4 is conveniently carried out by introduction of

  in an autoclave of isobutene and the compound I1, in an inert solvent, for example an aliphatic or aromatic hydrocarbon, and a quantity

  stoichiometrically, relative to the compound II, a tertiary amine.

  After stirring for a few hours at approximately 600 ° C., the reaction mixture

  is taken up and the compound III is isolated by distillation.

  The rearrangement of compound III to compound IV (reaction 5) can be obtained with good results by heating to about 100-1100C of a solution of compound III in an inert solvent, such as an aromatic hydrocarbon or dimethylformamide and in the presence of a quaternary ammonium salt or an aliphatic tertiary amine used as a catalyst. Compound IV is then isolated by distillation. Finally, by treating the compound IV in an inert solvent with one of the alkaline bases (reaction 6),

8 2499070

  Compound I is obtained which can be separated by acidification, extraction and distillation, or which can easily be converted to acyl halide.

  corresponding, and also isolated by distillation, in this form.

  If desired, the acyl halide derived from the compound I can easily be converted to the free acid I. However, for the preparation of pyrethroids, to which the compound I is intended, it is generally useful to have the acyl chloride

  corresponding which can be reacted directly with the alcohol con-

  venable, as stated above.

  With the aid of the process according to the present invention, compound I is obtained in a cis / trans isomer ratio (on the cyclopropane ring).

greater than 4/1.

  As far as is known, the polyhalogenated derivatives of pentanoic acid II, A and B (see scheme 3) can be grouped under the following general formula:

CF3 - CF - CH2 - CH - R

I I

X Y

  (in which: R '= Ct, Br, OH, ORi R = an alkyl radical comprising 1 to 4 carbon atoms; X and Y = Cl, Br), and the cyclobutanones III and IV are novel compounds which form in

  as such the subject of the present invention.

  Other advantages and features of the present invention

  will appear on reading the following description and given examples

  illustrative but nonclimitative.

EXAMPLE 1

  Preparation of 2,4-dibromo-4,5,5,5-tetrasulphonic acid methyl ester

  fluoro-pentanoic (reaction 2a, scheme 3):

CF3 - CFBr - CH2 - CHBr - COOCH3.

  In an autoclave equipped with a mechanical stirrer, 780 g are introduced.

  (3 moles) 1,1-dibromo-tetrafluoroethane (CF3-CFBR2) and 140 g of DMF.

  The autoclave is then closed and heated to 140 ° C. with constant stirring. A solution consisting of: - 1 mole of methylacrylate (CH2 = CH-COOCH3), - 5 moles of iron-pentacarbonyl [Fe (4), is introduced into the autoclave for 4 to 6 hours with the aid of a dosing pump. CO) 5]

260 g of CF3-CFBr2. -

  When the addition is complete, stirring is continued at the same temperature for a further two hours. After cooling, the reaction mass is then subjected to fractional distillation; the following fractions are collected: fraction I: 874 g (3.36 moles) of unreacted CF3CFBra; fraction II: 0.32 mole of unreacted acrylic ester; fraction III: 0.56 mol of the desired product (boiling point: 60 ° C. under 4.5 mm of mercury) (conversion of the acrylic ester: 68%;

  to the desired product based on the reacted acrylic ester: 82%).

  The structure of the product obtained is confirmed by the analysis below.

  red as well as by mass spectroscopy.

EXAMPLE 2

  The procedure is the same as that described in Example 1, and the following compounds are prepared: ethyl ester of 2,4-dibromo-4,5,5-tetrafluoro-pentanotacic acid

  (boiling point: 60 ° C at 3 mm Hg).

  n-butyl ester of 2,4-dibromo-4,5,5,5-tetrafluoro-pentanol

  (boiling point: 60 ° C at 0.2 mm Hg).

  For these two compounds, it is found that the results of infrared analysis and mass spectroscopy are in agreement with the expected structure.

EXAMPLE 3

  * Preparation of 2,4-dibromo-4,5,5-tetrafluoro-pentanoic acid (reaction 2b): CF3-CFBr-CH2-CHBr-COOn The preparation is carried out by trans-esterification of one of the

  esters described in Examples 1 and 2.

  In a reactor equipped with a fractionation column (corresponding to 3-4 theoretical plates), there is introduced: 1 mole of 2,4-dibromo-4,5,5,5-tetrafluoro pentanotacic acid ethyl ester; ml of concentrated H2SO0,

138 g (3 moles) of formic acid.

  The reaction mixture is then heated to boiling and maintained at this temperature for 8 to 10 hours, and the ethyl formate formed is removed from the top of the column. When the ethyl formate has been removed, the excess formic acid is removed, thereby obtaining as a residue a substantially stoichiometric amount of the acid.

  desired (boiling point: 65 ° C at 3 mm Hg).

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EXAMPLE 4

  * Preparation of 2,4-dibromo-4,5,5,5-tetrafluoro-1-pentanol (reaction 3a):

CF 3 CFBr - CH 2 - CHBr - CH 2 OH.

  In a glass autoclave swept by a stream of nitrogen, one introduces

  yield: 58 g (1 mole) of allyl alcohol (CH 2 = CH-CH 2 OH);

- 520g of CF3- CFBr2.

  The autoclave is then closed and heated to 130 C, after which

  introduced in 4 hours, a solution of 2 ml of Fe (CO) 5 in 60 ml of iso-

propanol.

  The mixture is then kept at rest for 1 hour at 130 ° C.

  When the mixture has been cooled, it is subjected to fractional distillation, and the fraction boiling at 56 ° C. under a pressure of 2 mm Hg is collected. It forms the desired product (170g) and presents

  a title in chromatography and gas phase of 93%.

  Data obtained by mass spectroscopy, magnetic resonance

  nuclear and infrared are in agreement with the planned structure.

EXAMPLE 5

  * Preparation of 2,4-dibromo-4,5,5,5-tetrafluoro-pentanofuc acid (reaction 3b): CF3-CFBr-CH2-CHBr -COOH In a thermostatic reactor, the following are introduced: - 182 nil of HN03 concentrated, - 0.8g of copper,

- 0.2g of V205.

  The mixture is heated to 70 ° C., then added with vigorous stirring and for a period of 15 minutes of a solution of 25.6 g of 2,4-dibromo-4,5,5,5-tetrafluoro-pentan-1-ol. (obtained as it is

  described in Example 4) in 40 ml of glacial acetic acid.

  The reaction mixture is then stirred at 70 ° C.

  additional minutes, after which the temperature is allowed to return to

  biante, then extract it with 300 ml of chloride

of methylene (CH2Cl2).

  The extract obtained is then washed with water (2 × 250 ml) and then dried over anhydrous Na 2 SO 4. The solvent is then removed by distillation under reduced pressure; 27 g of a residue consisting of the desired product are thus obtained (title of the gas-liquid phase chromatography

greater than 75%).

11 2499070

EXAMPLE 6

  Preparation of 2,4-dibromo-4,5,5,5-tetrafluoropentanoic acid chloride (reaction 2c or 3c): CF3-CFBr-CH2-CHBr-C-CL o 1 mole of 2,4-dibromo acid 4,5,5,5-tetrafluoro-pentanol (prepared according to the method described in Example 3 or 5) is heated at reflux together with 2 moles of thionyl chloride. After 4 hours, the mixture is cooled and then subjected to fractional distillation; a fraction whose boiling point is 55 ° C. under a pressure of 7 mm of mercury and which consists of chloride is thus collected.

  of acyl research (330g). IR spectrum: 1790 cm -1 (vC = O).

EXAMPLE 7

  * Preparation of the compound 2-bromo-2- (2'-bromo-2,3,3,3 ', 3'-tetraftuoropropyl)

  3,3-dimethylcyclobutanone (reaction 4):

H3C CH3

C CF3 - CFBr - CH2 / C

C CH2

  In an autoclave, provided with a mechanical stirrer, is introduced by suction: 320 g (5.71 moles) of isobutene [CH 2 = C (CH 3) 2];

400 ml of n-hexane.

  The reaction mixture is then heated to 100 ° C. and, with constant stirring, is introduced into the autoclave, separately:

  a solution of 100 g (0.2853 mol) of 2,4-dibromoacid chloride

  4,5,5,5-pentanoic acid (prepared according to the method described in Example 6) in 150 ml of n-hexane, and

  a solution of 29 g (0.2853 mol) of triethylamine in 160 ml of hexane.

  When the addition is complete, the reaction mixture is brought back

* at room temperature, after which it is filtered to separate the chlorine

triethylamine hydrate.

-12 2499070

  After evaporation of the excess isobutene and n-hexane, a residue of 103 g is obtained which is distilled off and from which the boiling fraction is collected at a temperature of -720C under 0.degree. 5 mm of mercury, and which consists of the desired product (85 g, title of the gas-liquid chromatography greater than 90%).

IR: 1791 cm -1 (vC = O).

  Fragmentation of the mass: 326 (j + - CH2 = C = O, main peak)

312 [M-CH 2 = C (CH 3) 2]

69.

EXAMPLE 8

  * Preparation of 2- (2'-bromo-2,3 '.3', 3'-tetrafluoropropyl) -3,3-dimethyl-

  4-bromo-cyctobutanone (reaction 5):

H3C CH3

C CF3 - CFBr - CH2-CH CH - Br

\ C

  I 0 -. In a solution of 1 g of tetrabutylammonium bromide [(C4H9), eNBr-] in 30 ml of DMF heated at 1100 C, is added over a period of 10 minutes.

  30 g of the cyclobutanone obtained according to the method described in Example 7.

  When the addition is complete, the reaction mixture is kept at the same temperature for 1 hour, after which it is allowed to warm to room temperature, then diluted in 50 ml of CH 2 Cl 2 and washed at room temperature.

  water until all of the DMF has been removed.

  The organic solution thus obtained is then dried over anhydrous Na 2 SO 4, and the solvent is removed by evaporation under reduced pressure; 24 g of a residue formed of two products which can be

  separated by fractional distillation.

  The fraction boiling in the range of 72 to 74 ° C

  under 0.5 mm of mercury (15g), it consists of the desired product.

IR: 1788 t cm -1 (vC = O).

  Fragmentation of mass: 288 (M - Br) 260 (M - HBr - CO) 248 (M - CHEr = C - OO) 134 [CHBr = C (CH3) 2, main peak)]

69 (CF)

(C4H7).

  The fraction whose boiling point is between 43 and 47 ° C., under 0.4 mm of mercury (4 g), corresponds to the product having the formula:

H3C. CH

C CF3 - CFBr-CH2 - CH CH2 I

0

IR = 1786 cm -1 (vC = 0).

Fragmentation of mass:

248 (M - CH 2 = C = O)

211 (M - Br) 69 (main peak) 55.

EXAMPLE 9

  * Preparation of 2- (2'-bromo-2 ', 3', 3,3-tetrafluoropropyl) -3,3-dimethyl-

  4-bromo-cyclobutanone (reaction 5).

  To a solution of 25 g of the cyclobutanone obtained according to the method described in Example 7 and dissolved in 50 ml of toluene heated to C, is added dropwise, over a period of 1 hour, a solution of 5 ml of tri ( n) butylamine [(n.C4H9) 3N] in 10 ml of toluene. After the addition has been completed, the reaction mixture is refluxed for a further hour, after which it is cooled to room temperature and washed with acidic water.

  make it anhydrous by passing over Na 2 SO 4, anhydrous.

  After removal of the solvent, under reduced pressure, the crude product is distilled off and the fraction which boils at 70 ° C. under 0.4 mm of mercury (22 g) and which is in agreement with the desired product (the infrared spectrum and the spectrometry mass are in agreement with

the planned structure).

EXAMPLE 10

  Preparation of 2,2-dimethyl-3- (e-fluoro-e-trifluoromethylvinyl) acid

  cyclopropanecarboxylic acid (reaction 6):

H3C CH3

oc -IC

CF3 - CF = CH: - CH CH - COOH

  To a solution of 4 g of NaOH in 60 ml of water, 15 g of

  4-bromo-cyclobutanone obtained as described in Example 8 or 9.

  The mixture is then stirred at room temperature during

  2h, then-during 2h additional to 100 C.

  After cooling to room temperature, the mixture is acidified by addition of hydrochloric acid to a concentration of 10% and then subjected

  extraction with CH2Cl2 (3 x 50 ml).

  The organic phase is then dried over anhydrous Na 2 SO 4 and the solvent is

  removed by evaporation under reduced pressure.

  A crude product is thus obtained which is purified by distillation.

  from which the fraction boiling at 63-65 ° C is collected.

  under 0.2 mm of mercury (89) which is in agreement with the desired product.

  Gas chromatography and the nuclear magnetic resonance spectrum show that the cyclopropane ring has the following isomeric structure: - cis isomer: 92%

trans isomer: 8%.

  Of course, the present invention is not limited to

  examples and modes of implementation mentioned above; she is sus-

  can be many variants accessible to those skilled in the art, according to the intended applications and without one deviates from the spirit of the invention.

Claims (4)

  1.- Process for the preparation of 2,2-dimethyl43- (e-fluoro-e-trihydric acid)   fluoromethyl-vinyl) -cyclopropanecarboxylic acid, having the formula: H3C CH3 CF3 CC "C = CH - CH - CH - COOH ( ff   characterized in that a halide (chloride or bromide) of 2,4-di-   halo-4,5,5,5-tetrafluoro-pentanol, of formula: -CF3 - CF - CH2 - CH - C - Z I I I X Y O (II)   (In which X, Y and Z, identical or different from each other, represent a chlorine or bromine atom) is reacted with isobutene in the presence of a base and an inert solvent. in order to lead to 2-halo-cyclobutanone (II), of formula: H3C X CH3 C CF3-CF-CH2-C CH: III) / \ C /   x Y I o which, by heating in an inert solvent and in the presence of a salt of ammonia   quaternary amine or a tertiary aliphatic amine, is re-arranged into 4-halogen cyclobutanone (IV) of formula: H3C CH3   C CF3-CF-CHa-CH CH-Y vI \ c / x I o which, in turn, by treatment with alkaline bases and in an inert solvent leads to the compound I.   2. Process according to claim 1, characterized in that the isomerization   Compound III to compound IV is obtained by treating compound III with a quaternary ammonium salt dissolved in dimethylformamide. -110 C.   3. A process according to claim 1, characterized in that the isomerization of compound III to compound IV is obtained by treatment of compound III   by a tertiary amine dissolved in toluene at the reflux temperature.   4. A process according to claim 1, characterized in that in the   Compounds II, III and IV, the substituents X and Y are bromine atoms.