Processes for preparing pesticidal intermediates

Details Processes for preparing pesticidal intermediates Processes for preparing pesticidal intermediates

2000-05-17

2001-07-10

McKane, Joseph K. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Nitriles

C558S394000

Reexamination Certificate

active

06258973

ABSTRACT:

This invention relates to processes for preparing pesticidal intermediates, and to novel 2-arylhydrazonosuccinonitrile compounds and to 2-arylhydarylhydrazinosuccinonitrile compounds.
European Patent Publication Nos. 0295117 and 0234119 describe the preparation of pesticidally active phenylpyrazole compounds and of 5-amino-1-aryl-3-cyanopyrazole intermediate compounds used in their synthesis. Various methods for preparing these compounds are known. It is, however, desirable to provide improved methods for the preparation of these compounds and the intermediate compounds thereto.
Arylhydrazines are known to undergo Michael addition with electron deficient alkenes such as acrylonitrile in polar protic solvents such as alcohols, and subsequent oxidation in a basic medium affords 5-amino-1-arylpyrazoles as described, for example, in U.S. Pat. No. 4,824,960. However, the applicants are not aware of any literature reports describing the reaction of hydrazines with fumaronitrile. The oxidation of N,N
1
-diarylhydrazines to azo compounds is known. N-Alkylhydrazines and N-arylhydrazines which are substituted on one nitrogen atom only are also oxidized to azo compounds but these are generally unstable, decomposing to nitrogen and hydrocarbons; see J. March,
Advanced Organic Chemistry,
3rd edition, page 1062. Y. H. Kim and Y. Choi describe in
Tetrahedron Letters,
Vol 37, pages 8771-4, 1996, the palladium catalyzed dehydrogenation of alpha-hydrazinonitriles in the presence of cyclopentene to give hydrazonyl cyanides. However, the applicants are unaware of any other references concerning the oxidation of hydrazines to hydrazones. Moreover, the Kim and Choi publication is restricted to the oxidation of unsubstituted phenyl hydrazine derivatives and no suggestion is made that the oxidation of hydrazine derivatives of fumaronitrile may be achieved.
It is a first object of the present invention to provide a convenient process for preparing 5-amino-1-aryl-3-cyanopyrazole pesticidal intermediates which are obtained in high yield and high purity.
It is a further object of the present invention to provide processes for the preparation of 2-arylhydrazonosuccinonitrile compounds which may be used to prepare said 5-amino-1-aryl-3-cyanopyrazole pesticidal intermediates.
It is a yet further object of the present invention to provide a process for the preparation of 2-arylhydrazinosuccinonitrile compounds.
It is a still further object of the present invention to provide novel intermediates in the manufacture of pesticidally active compounds.
These and other objects of the invention will become apparent from the following description, and are achieved in whole or in part by the present invention.
In one aspect, the present invention provides a process for the preparation of a compound of formula (I) by the cyclization of a compound of formula (II), according to the reaction scheme Sc 1 indicated below:
wherein W is nitrogen or —CR
4
; R
2
, R
4
, R
5
and R
6
are independently selected from hydrogen, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, R
7
S(O)
n
—, nitro, cyano and —SF
5
; and R
3
is as defined for R
2
, or is phenyl optionally substituted by one to five members of the group consisting of halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, R
7
S(O)
n
—, nitro, cyano and —SF
5
, which are the same or different; R
7
is alkyl or haloalkyl; and n is 0, 1 or 2.
Unless otherwise specified in the present specification, ‘alkyl’ means straight- or branched-chain alkyl having from one to six carbon atoms (preferably one to three). Unless otherwise specified, ‘haloalkyl’ and ‘haloalkoxy’ are straight- or branched-chain alkyl or alkoxy, respectively, having from one to six carbon atoms (preferably one to three) substituted by one or more halogen atoms selected from fluorine, chlorine and bromine.
Preferred compounds of formula (I) are those having one or more of the following features: R
2
is halogen or hydrogen; R
3
represents halogen, haloalkyl (preferably trifluoromethyl), haloalkoxy (preferably trifluoromethoxy), R
7
S(O)
p
—, —SF
5
, or phenyl substituted by one to three members of the group consisting of trifluoromethyl, trifluoromethoxy, difluoromethyl, —S(O)
n
CF
3
, dichlorofluoromethyl, chlorodifluoromethyl, chlorodifluoromethoxy, dichlorofluoromethoxy and halogen which may be the same or different; R
4
is halogen; and R
5
and R
6
are hydrogen.
Especially preferred compounds of formula (I) are those having one or more of the following features:
W represents —CR
4
and R
4
is halogen;
R
3
represents haloalkyl, haloalkoxy or —SF
5
; and
R
5
and R
6
represent hydrogen.
Most preferably, the compound of formula (I) is 5-amino-3-cyano-1-(2,6-dichloro-4-trifluoromethylphenyl)pyrazole.
The above reaction Sc 1 to obtain compounds of formula (I) is generally performed in the presence of a base, which may be organic or inorganic. Examples of suitable organic bases are amines such as triethylamine or pyridine. Examples of suitable inorganic bases are alkali or alkaline earth metal hydroxides, acetates, carbonates or bicarbonates such as sodium hydroxide or sodium carbonate, or preferably ammonia (aqueous or gaseous). Generally, the molar ratio of the compound of formula (I):base is from about 1:10, to about 10:1. The reaction is optionally carried out in the presence of a phase transfer catalyst, for example, quaternary ammonium salts such as benzyl trimethylammonium chloride, tricaprylylmethylammonium chloride, tetramethylammonium chloride, tetra-n-propylammonium bromide, n-dodecyl trimethylammonium chloride, tetra-n-butylammonium chloride, and n-tetradecyl trinethylammonium bromide. The reaction is generally performed in a solvent, and suitable solvents include alcohols (preferably ethanol) or non water-miscible solvents, especially halogenated hydrocarbons such as dichloroethane or dichloromethane, non-miscible solvents being appropriate when a phase transfer catalyst is employed. Optionally water may be used as a co-solvent. The reaction temperature is generally from about −20 to about 50° C. and preferably from about 0 to about 20° C.
According to a further feature of the present invention, there is provided a process for the preparation of a compound of formula (II) by the oxidation of a compound of formula (III), according to the reaction scheme Sc 2 indicated below:
wherein W, R
2
, R
3
, R
5
and R
6
are as defined above.
The preferred compounds of formula (II) are as defined for the definition of W, R
2
, R
3
, R
5
and R
6
for compounds of formula (I) above. The most preferred compound of formula (II) is 2-(2,6-dichloro-4-trifluoromethylphenylhydrazono)succinonitrile.
Compounds of formula (II) may be obtained as a mixture of syn and anti isomers and all such forms are embraced by the present invention.
Suitable oxidants for the above reaction scheme Sc 2 to form compounds of formula (II) include quinones such as benzoquinone, peroxides such as hydrogen peroxide, hypohalites such as sodium hypochlorite, or an alkali metal hydroxide such as sodium hydroxide in the presence of air, or preferably a metal salt or oxide, for example, cupric chloride or mercuric oxide. The reaction is generally conducted in a solvent. Solvents suitable for use include aromatic halogenated or non-halogenated hydrocarbons such as toluene or chlorobenzene, nitriles such as acetonitrile or amides such as N,N-dimethylformamide. The reaction temperature is generally from about 20 to about 150° C., and preferably from about 50 to about 100° C.
According to a further feature of the present invention, there is provided a process for the preparation of a compound of formula (II) by the reaction of a compound of formula (IV), an enol thereof, or an enolate salt thereof, with a diazonium salt of formula (V) according to reaction scheme Sc 3 below:
wherein W, R
2
, R
3
, R
5
and R
6
have the same meaning as defined above in reaction scheme Sc 1 and X is generally an anionic group from a mineral acid such as hydrogen sulfate or chloride.
The compound (IV) is generally in the form of an enolate salt, preferabl

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