Preparation of 3,5-diarylpyrazoles

Details Preparation of 3,5-diarylpyrazoles Preparation of 3,5-diarylpyrazoles

1997-07-03

1998-04-28

Richter, Johann

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

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C07D23112

Patent

active

057446148

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP96/00011 filed Jan. 4, 1996.
The present invention relates to a novel process for preparing 3,5-diarylpyrazoles of the general formula I ##STR3##
where the substituents have the following meanings:
R.sup.1 and R.sup.3 are unsubstituted or substituted aryl radicals, R.sup.2 is hydrogen, C.sub.l -C.sub.8 -alkyl or unsubstituted or substitued aryl.
3,5-Diphenylpyrazole can be prepared by reaction of diphenylpropane-1,3-dione (dibenzoylmethane) with hydrazine hydrate, which is described, for example, in U.S. Pat. No. 3,882,142.
Furthermore, the reaction of benzylideneacetophenone dibromide with hydrazine hydrate leads to 3,5-diphenylpyrazole (Freudenberg, Stoll, Justus Liebigs Ann. Chem., 440 (1924), 45).
Other possibilities of preparation are dehydrogenations of 3,5-diphenylpyrazolines by, for example, catalytic dehydrogenation according to U.S. Pat. No. 4,014,896, U.S. Pat. No. 3,952,010 and DE 24 41 504.
The appropriate pyrazolines can be obtained by reacting chalcones (1,3-diarylpropenones, eg. benzylideneacetophenone) with hydrazine hydrate in alcoholic solution (Kishner Zh. Russ. Fiz.-Khim. O-va 47 (1915) 1102; Centralblatt, 1916 I, 1063).
A further possibility of synthesis of 3,5-diphenylpyrazoline is the reaction of phenylphenylacetylenylcarbinol with hyrazine hydrate (Stoll, Justus Liebigs Ann. Chem., 440 (1924), 39, 42).
In addition to the preparation of pyrazoles by dehydrogenation of 3,5-disubstitued pyrazolines, U.S. Pat. No. 4,014,896, U.S. Pat. No. 3,952,010 and DE 24 41 504 also describe the synthesis of the latter by reaction of 1,3-disubstituted propenones with hydrazine hydrate. The procedure used here is in general one in which a methyl aryl ketone, eg. acetophenone, is reacted with benzaldehyde in methanol in the presence of bases to give the corresponding 1,3-disubstituted propenones which, after acidifying with mineral acids, react with hydrazine hydrate to give the desired pyrazolines.
EP 402 722 discloses a further process for preparing pyrazole by dehydrogenation of 2-pyrazoline.
Since the pyrazole syntheses described are multistage syntheses, the object was therefore to make 3,5-diarylpyrazoles accessible in a technically simpler and more economical manner.
Accordingly, a process has been found for preparing 3,5-diarylpyrazoles of the general formula I ##STR4##
where the substituents have the following meanings:
R.sup.1 and R.sup.3 are unsubstituted or substituted aryl radicals, R.sup.2 is hydrogen, C.sub.1 -C.sub.8 -alkyl or unsubstituted or substituted aryl, in which hydrazine hydrate is reacted with a 1,3-diarylpropenone of the general formula II ##STR5##
where the substituents R.sup.1, R.sup.2 and R.sup.3 have the abovementioned meanings, in sulfuric acid in the presence of iodine or an iodine compound.
It has furthermore been found that instead of 1,3-diaryl-propenones of the general formula II, their starting compounds, a carbonyl compound of the general formula III ##STR6##
and an arylaldehyde of the general formula IV
where the substituents R.sup.1, R.sup.2 and R.sup.3 have the abovementioned meanings, can be used.
The reaction proceeds in a one-pot process.
The 1,3-disubstituted pyrazoline formed from hydrazine hydrate and the appropriate 1,3-diarylpropenone of the formula II or its starting substances, the carbonyl compound of the formula III and arylaldehyde of the formula IV, is dehydrogenated in the reaction mixture to the corresponding 3,5-diarylpyrazole by the iodine formed from hydrogen iodide and sulfuric acid, corresponding amounts of sulfur dioxide being liberated by the oxidation of hydrogen iodide to iodine by sulfuric acid. The reactants hydrazine hydrate and 1,3-diarylpropenone of the formula II or their starting substances, the carbonyl compound of the formula III and arylaldehyde of the formula IV, are reacted in stoichiometric amounts, it being possible to employ the reactants in an excess or insufficient amount.
The sulfuric acid, which is employed as an oxidant and also as a diluent, is in general employed in a from 0.5-

REFERENCES:
patent: 3952010 (1976-04-01), Garber et al.

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