Process for preparing sulphurous 2-chloro-3-(4,5-dihydroisoxazol

Details Process for preparing sulphurous 2-chloro-3-(4,5-dihydroisoxazol Process for preparing sulphurous 2-chloro-3-(4,5-dihydroisoxazol

1999-07-13

2000-09-26

Lambkin, Deborah C.

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C07D26118

Patent

active

061244694

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for preparing sulfur-containing 2-chloro-3-(4,5-dihydro-3-isoxazolyl)benzoic acids of the formula I ##STR1## where the substituents have the following meanings: n 0, 1 or 2; -haloalkyl or which may be substituted once to four times by C.sub.1 -C.sub.4 -alkyl.
The invention furthermore relates to the intermediates essential for this process: the alkylthiobenzoic acids of the formula Ia, bromo thioethers of the formula V, thioethers of the formula IV and 3-(2,6-dichlorophenyl)isoxazolines of the formula II.
WO 96/26200 has disclosed a-nine-stage process for preparing methyl 2-chloro-3-(4,5-dihydro-3-isoxazolyl)-4-methylsulfonylbenzoate in which the isoxazoline unit is assembled only toward the end of the synthetic sequence.
WO 96/26200 furthermore mentions 2,4-disubstituted 3-(heterocyclyl)benzoic acids as intermediates for herbicides. WO 95/14680 and EP-A 245 825 describe 3-phenylisoxazolines which may be substituted twice or three times in the phenyl nucleus as pharmaceuticals.
It is an object of the present invention to find a shorter route, which is less costly and can be used on an industrial scale to sulfur-containing 2-chloro-3-(4,5-dihydro-3-isoxazolyl)benzoic acids of the formula I.
We have found that this object is achieved by the process which is mentioned at the outset and which provides the required sulfur-containing 2-chloro-3-(4,5-dihydro-3-isoxazolyl)benzoic acids of the formula I in good yields (scheme 1). Alkylthiobenzoic acids of the formula Ia can thus be obtained in three stages starting from 3-(2,6-dichlorophenyl)isoxazolines of the formula II or in five stages starting from 2,6-dichlorobenzaldehyde which can be bought. An oxidation step then results in the alkylsulfonyl- or alkylsulfinylbenzoic acids of the formula Ib. ##STR2##
The process according to the invention can be used to prepare sulfur-containing 2-chloro-3-(4,5-dihydro-3-isoxazolyl)benzoic acids of the formula I. The meanings specified above for the substituents R.sup.1 to R.sup.4 in formula I are collective terms for individual lists of members of individual groups. All the carbon chains, that is to say all the alkyl moieties, can be straight-chain or branched. Halogenated substituents preferably have 1-6 identical or different halogen atoms.
Examples of specific meanings are: 2-methylpropyl and 1,1-dimethylethyl; 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1-ethyl-1-methylpropyl and 1-ethyl-2-methylpropyl; completely substituted by fluorine, chlorine and/or bromine, eg. chloromethyl, dichloromethyl, trichloromethyl, fluoromethyl, difluoromethyl, trifluoromethyl, chlorofluoromethyl, dichlorofluoromethyl, chlorodifluoromethyl, 1-fluoroethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 2-chloro-2-fluoroethyl, 2-chloro-2,2-difluoroethyl, 2,2-dichloro-2-fluoroethyl, 2,2,2-trichloroethyl, pentafluoroethyl and 3-chloropropyl, preferably trifluoromethyl.
Particularly preferred alkylthiobenzoic acids of the formula I, bromo thioethers of the formula V, thioethers of the formula IV and 3-(2,6-dichlorophenyl)isoxazolines of the formula II are those where the substituents R.sup.2 to R.sup.4 are each hydrogen.
The process can also, because of the reagents used and the reaction conditions, be used on an industrial scale (can be scaled up).
We have furthermore found sulfur-containing 2-chloro-3-(4,5-dihydro-3-isoxazolyl)-benzoic acids of the formula Ia, bromo thioethers of the formula V, thioethers of the formula IV and the 3-(2,6-dichlorophenyl)isoxazolines of the formula II which are suitable as intermediates.
The thioethers of the formula IV required in the process according to the invention can be prepared in various ways (scheme 2). Route C therein is particularly preferred because the thiolys

REFERENCES:
Monatsheft fur Chemie 99 (1968), pp. 815-822.

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