Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1998-01-20
1999-11-16
Barts, Samuel
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
560124, 549302, C07C 6104
Patent
active
059861304
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to compounds usable as intermediates in the preparation of cyclopropane carboxylic esters, and the invention also relates to processes for preparing these compounds.
Cyclopropane carboxylate esters are insecticidally active compounds which are known as "pyrethroids", and since they combine exceptionally good insecticidal properties with very low toxicity to mammals they are of considerable interest. Therefore, much effort has been made in order to find economically favourable routes for preparing them and their most important intermediates. ##STR1##
One class of these pyrethroid compounds showing a remarkably high activity has the general formula I where the carbon atoms marked 1 and 3 are asymmetrical carbon atoms, and R' is selected from a group of radicals known to impart an insecticidal activity to the molecule, e.g. RS-.alpha.-cyano-3-phenoxybenzyl or S-.alpha.-cyano-3-phenoxybenzyl or 2-methylbiphenyl-3-ylmethyl or 2,3,5,6-tetrafluoro-4-methylbenzyl.
The superscripts .sup.1, .sup.2 etc. in the following description refer to the list of references at the end of the present description.
It is known.sup.1 that the stereoisomeric configuration of the acid moiety of the ester Ia should have the geometry 1R, cis, Z in order to obtain maximum insecticidal activity, i.e. the absolute configuration at carbon atom 1 is R, the two hydrogen atoms at carbon atoms 1 and 3 are in cis-position, and the chlorine atom and cyclopropane group are at the same side of the carbon-carbon double bond.
Therefore, it is of great importance to be able to prepare the active isomer of I in a technically as well as economically attractive manner in order to minimize in this way the applied amount of active substance (insecticide) in the treatment of agricultural crops, habitations and the like.
From this it follows that if such compounds of formula Ia are to be prepared, it is necessary either to provide a stereospecific chemical synthetic route or to isolate the desired stereoisomer from a racemic mixture by physical separation techniques. The latter method is normally expensive and rarely used on an industrial scale.
It is known.sup.2 that Biocartol of formula II below can be reacted with a halogenated one-carbon compound such as CHBr.sub.3, CHCl.sub.3 eller CHClF.sub.2 in the presence of a strong base to obtain cyclopropane carboxylic acid derivatives.
It is also known.sup.3 that the racemic compound of formula IVb below can be prepared by cyclizing 4-diazoacetoxy-5,5-dichloro-6,6,6-trifluoro-2-methyl-2-hexene in a suspension of copper(II)acetyl acetonate in boiling dioxane where the cyclopropane ring is thus formed as the last step in a reaction sequence.
Moreover, it is suggested.sup.3 that the racemic compound of formula IVb below can be formed by reaction between esters of cis-3-formyl-2,2-dimethyl-cyclopropane carboxylic acid and 1,1,1-trichloro-2,2,2-trifluoro-ethane in the presence of zinc.
A route has now been found to the commercially important compounds of the type I where as starting material use is made of the substance Biocartol (formula II) which is easily prepared in an optically pure form IIa from the naturally occurring substance (+)-3-carene.sup.4,5,6 or in a racemic form IIb via ozonolysis of chrysanthemic acid or derivatives thereof.sup.3. Trans-3-(dimethoxymethyl)-2,2-dimethyl-cyclopropane carboxylic acid methyl ester which is commercially available from, e.g., Aldrich-Chemie, is also via hydrolysis and epimerization-lactonization a source of IIb.
This synthetic route is quite specific in respect of the stereoisomery of the products such that the geometry of IIa can be found again in the product Ia. In this way costly racemate resolutions as well as yield losses to useless isomers are avoided. ##STR2## Here is described a number of new syntheses (see Reaction Scheme) of the (1R, cis, Z)-acid moiety in the pyrethroid esters of formula Ia (R'=H) from Biocartol IIa, going via novel intermediates IIIa and/or IVa of the invention. These synthetic methods can be used in the same way
REFERENCES:
patent: 4230891 (1980-10-01), Verbrugge et al.
patent: 4281182 (1981-07-01), Martel et al.
patent: 4333950 (1982-06-01), Engel
Chem Abstracts 109:190585, Fujita et al., 1987.
M. Fujita, et al., Tetrahedron Letters, vol. 27, No. 19, 1986, pp. 2139-2141.
M. Fujita, et al., Bull Chem. Soc., vol. 60, 1987, pp. 4385-4394.
A. K. Mandal, et al., Tetrahedron, 42, 5715, (1986).
D. Bakshi, et al., Tetrahedron, 45, 767-774, (1989).
Klemmensen Per Dausell
Kolind-Andersen Hans
Winckelmann Ib
Barts Samuel
Cheminova Agro A/S
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