A process for the preparation of 1-alkyl-3-carboxy-4-cinnolones.

Abstract: A process for the preparation of 1-alkyl-3-car­ boxy-4-cinnolones of formula I wherein R and R₁ are electron donor groups and R₃ is an alkyl group, starting from an amine of formula II which is subjected to the following transformations; 1) diazotation; 2) coupling with a cyanoacetic ester; 3) alkylation of the arylhydrazone obtained in 2); 4) hydrolysis of the ester and conversion into acyl chloride; 5) intramolecular cyclization; 6) hydrolysis of the nitrile residue.

Description: The present invention relates to a process for the preparation of 1-alkyl-3-carboxy-4-cinnolones of formula I wherein R and R₁, which may be the same or different, are hydrogen or electron donor groups such as alkoxy or alkylthio groups, or, taken together, are a methylenedioxy group; R₃ is a C₁-C₆ alkyl group. The invention also relates to novel intermediates useful for the preparation of compounds I. Compounds of formula I, particularly 1-ethyl-3-carboxy-6,7-methylenedioxy-4-cinnolone (Formula I, wherein R + R₁ = methylenedioxy, R₃ = ethyl), are known therapeutic agents having antibacterial activity. The processes hitherto known (DE-2005104) suffer from some drawbacks such as the use of toxic and dangerous reactants (bromine, cyanides) and the formation of by-products which are difficult to be removed, with a consequent decrease in the yields. The process according to the invention allows to overcome the drawbacks of the prior art, said process being characterized by few steps, high yields and use of reactants which are not particularly dangerous. The process according to the invention is summarized in the following scheme. In the above formulae, R and R₁ have the above mentioned meanings, R₂ is C₁-C₄ straight or branched alkyl group and R₃ is a C₁-C₆ straight or branched alkyl group or a C₃-C₆ cycloalkyl group. Compounds of formulae, V and VI are novel and form a further object of the invention. Arylazocyanoacetic esters III are prepared according to known methods, by coupling the diazo-compound of an arylamine II with a cyanoacetic acid ester. Subsequent alkylation of esters III is carried out with alkylating agents R₃X, wherein R₃ has the above mentioned meanings and X is an halogen atom or a sulfate residue, in a preferably polar aprotic solvent and in the presence of bases. Alkali carbonates, such as K₂CO₃ or Na₂CO₃ are used as bases, while appropriate solvents are lower aliphatic ketones, dimethylformamide, methylpyrrolidone, acetonitrile. The preferred reaction temperatures range from 10° to 100°C, more preferably from 30° to 40°C, for the times necessary to complete the reaction. It is often appropriate to use an excess of the alkylating agent, whether the alkylation conditions may involve, as a side reaction, hydrolysis of a part of the alkylating agent itself. Hydrolysis of compound IV to give compounds V is preferably effected using (in stoichiometric ratios) an alkali hydroxide such as NaOH or KOH, in the presence of a water-miscible solvent such as an alcohol, at temperatures from 0° to 80°C, preferably 20° to 30°, for time sufficient for the hydrolysis to be completed. Carbon-alkylated products (arylazo-alkyl-cyanoacetic esters) which are not hydrolyzed in the selected conditions can easily be removed before chlorination, since they are not water-soluble. Acids V are then transformed into corresponding acyl chlorides VI by reaction with a chlorinating agent such as SOCl₂, PCl₃, PCl₅ in such appropriates solvents as benzene, toluene, chloroform, methylene chloride, chlorobenzene, usually working under reflux until gas evolution is over. Intramolecular cyclization to compounds VII is surprisingly carried out by simple heating, in the absence of Lewis acids, for instance by refluxing the acyl chloride in an appropriate inert solvent, at a temperature ranging from 100° to 150°C, until HCl evolution is over. Under such conditions, yield are high and formation of resinous by-products is not observed. In case substituents R and R₁ on the ring are electron donors enough, e.g. for the methylenedioxy residue, chlorination of acids V and subsequent cyclization may be carried out in a single step, by suitably selecting the solvent. Conversion of nitrile into the final product is eventually effected by acid hydrolysis, according to known methods. The following examples further illustrate the invention. EXAMPLE 1 Ethyl 3,4-methylenedioxyphenylazocyanoacetate (III). 3.1 kg of 3,4-methylenedioxyaniline hydrochloride were dissolved in 9 l of water + 3 l of conc. HCl. A solution of 1.32 kg of NaNO₂ in 4 l of water was slowly added, cooling to 0°C in outer bath. The resulting diazo solution was added under stirring, during 1 hour 30, again at 0°C, to a solution obtained mixing 1.3 l of water, 2.7 l of acetic acid, 4 l of 30% (w/w) NaOH, 9 l of ethanol and 2.31 kg of ethyl cyanoacetate. Temperature was left to gradually rise to 15°C during 2 hours, then the precipitate was filtered and washed twice with 15 ml of ethanol at 0°C. Yield: 90% on theor.; m.p. 115-118°C; orange product, which may be recrystallized from ethanol. By the same procedure, using methyl cyanoacetate, the corresponding methyl ester was obtained, m.p. 177°C. EXAMPLE 2 Ethyl 3,4-methylenedioxyphenyl-N'-ethyl-phenylhydrazono-cyanoacetate (IV). 2.15 kg of dry powdered K₂CO₃ and 6.8 kg of diethyl sulfate were added to 4.35 kg of the thoroughly dried compound of example 1 in 3 ℓ of acetonitrile. The mixture was refluxed for 5 hours with stirring, cooled to 20°, and the precipitate was filtered and washed twice with acetonitrile (2.5 l each time). The filtrate was evaporated to dryness under vacuum and the residue was treated with 2 l of isopropanol. The mass was stirred for 1 hour and the crystals were filtered and washed 3 times with 0.5 l of isopropanol cooled to 0°C. 2.7 kg of the pure compound were obtained, m.p. 78-80°C, of yellow colour, which can be recrystallized from ethanol. By the same procedure, using the corresponding methyl ester, the corresponding ethylation compound was obtained, melting at 129-131°C. EXAMPLE 3 Acid 3,4-methylenedioxyphenyl-N'-ethyl-phenylhydrazono-cyanoacetic acid (V). 1.84 kg of the ester prepared according to example 2 were suspended in 5.4 l of ethanol and 5.6 l of water and 6.3 l of 30% (w/w) of NaOH were added thereto. The mixture was stirred at room temperature for 20 hours, then ethanol was removed by concentration under reduced pressure. Upon acidification with HCl of the filtered solution, a product separated in form of a gum, which slowly solidified. The crude filtrate was ground and washed with some ethyl acetate. Yield: 1.5 kg of product, which was purified by dissolution in diluted alkali, filtration with charcoal and reprecipitation with acetic acid. Yellow product, m.p. 131-133°C. The same compund was obtained, according to the same procedure, from the corresponding methyl ester. EXAMPLE 4 3,4-methylenedioxyphenyl-N'-ethyl-phenylhydrazono-cyanoacetic acid chloride (VI). 2 kg of thionyl chloride were added to 3 kg of the acid described in example 3, thoroughly dried and ground, suspended in 1,5 l of dichloroethane. The mixture was refluxed for 5 hours, then the solution added with some decolorizing carbon was filtered and left to crystallize overnight at 0°C. The separated acyl chloride was filtered. Some more product was recovered by concentration of mother liquors. 2.4 kg of compound were obtained, m.p. 170°C with decomposition (75% on theor.). EXAMPLE 5 1-ethyl-3-cyano-6,7-methylenedioxy-4-cinnolone (VII). 7.5 kg of acyl chloride, prepared according to example 4, were suspended in 10 l of chlorobenzene and refluxed under stirring, refluxed for 6 hours, then cooled to 0°C for 3 hours. Crystals were filtered and washed with some methylene chloride. 5.5 kg of compound were obtained, unitary by TLC, (m.p. 265°C), which was colorless and poorly soluble in common solvents. Alkali hydrolysis of this nitrile, according to the method already described in literature, gives the corresponding acid. EXAMPLE 6 1-ethyl-3-cyano-6,7-methylenedioxy-4-cinnolone (VII). 75 kg of the compound prepared as described in example 3, thoroughly dried, were suspended into 1000 l of chlorobenzene. 52 kg of thionyl chloride were added to the suspension, which was gradually heated to reflux to 80°C, keeping this temperature for about 10 hours. A partial vacuum was then applied and 750 l of chlorobenzene were distilled at about 50°-80°C; then vacuum was interrupted and the solution was refluxed (about 135°C) for about 6 hours. The solution was then cooled to 0°C, the separated solid was filtered and washed twice in centrifuge with 50 l each time of methylene chloride. The solid was washed with 300 ml of methylene chloride under stirring for 30 min., refiltered and dried. Yield: 54 kg (79%) of compound, unitary in TLC.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, IT, LI, LU, NL, SE A process for the preparation of cinnolones of formula I wherein R and R₁, which may be the same or different, are hydrogen or electron donor groups such as alkoxy or allylthio groups, or, taken together, are a methylenedioxy group; R₃ is a C₁-C₆ alkyl group or C₃-C₆ cycloalkyl, which process comprises: a) reaction of a compound of formula II wherein R and R₁ are as above defined, with an alkali nitrite in acid medium, followed by reaction with a cyanoacetic acid ester of formula CN-CH₂-COOR₂ (R₂=C₁-C₄ alkyl), to give a compound of formula III b) alkylation of compound III with an alkylating agent R₃X (X=halogen, or a sulfate residue and R₃ = C₁-C₆ alkyl or C₃-C₆ cycloalkyl), in the presence of bases, to give compound IV c) hydrolysis of ester IV to carboxylic acid V, transformation of the latter into acyl chloride VI and intramolecular cyclization to compound VII d) acid hydrolysis of compound VII to compound I. A process according to claim 1, wherein R and R₁, taken together, form a methylenedioxy ring. A process according to claims 1-2, wherein R₂ is CH₃ or C₂H₅. A process according to any one of the preceding claims, wherein R₃ is C₂H₅ and X is a sulfate residue. A process according to any one of the preceding claims, wherein intramolecular cyclization is carried out by heating in chlorobenzene, at a temperature from 100 to 150°C, in the absence of Lewis acids. A compound of formula V or VI wherein R and R₁, taken together, are a methylenedioxy group, R₃ is a C₁-C₆ alkyl group. A process according to the claims 1-5, steps a)-c) for the synthesis of 1-ethyl-3-cyano-6,7-methylenedioxy-4-cinnolone. Claims for the following Contracting States : ES, GR A process for the preparation of cinnolones of formula I wherein R and R₁, which may be the same or different, are hydrogen or electron donor groups such as alkoxy or alklthio groups, or, taken together, are a methylenedioxy group; R₃ is a C₁-C₆ alkyl group or C₃-C₆ cycloalkyl, which process comprises: a) reaction of a compound of formula II wherein R and R₁ are as above defined, with an alkali nitrite in acid medium, followed by reaction with a cyanoacetic acid ester of formula CN-CH₂-COOR₂ (R₂=C₁-C₄ alkyl), to give a compound of formula III b) alkylation of compound III with an alkylating agent R₃X (X=halogen, or a sulfate residue and R₃ = C₁-C₆ alkyl or C₃-C₆ cycloalkyl), in the presence of bases, to give compound IV c) hydrolysis of ester IV to carboxylic acid V, transformation of the latter into acyl chloride VI and intramolecular cyclization to compound VII d) acid hydrolysis of compound VII to compound I. A process according to claim 1, wherein R and R₁, taken together, form a methylenedioxy ring. A process according to claims 1-2, wherein R₂ is CH₃ or C₂H₅. A process according to any one of the preceding claims, wherein R₃ is C₂H₅ and X is a sulfate residue. A process according to any one of the preceding claims, wherein intramolecular cyclization is carried out by heating in chlorobenzene, at a temperature from 100 to 150°C, in the absence of Lewis acids. A process according to the claims 1-5, steps a)-c), for the synthesis of 1-ethyl-3-cyano-6,7-methylenedioxy-4-cinnolone.

Inventors: BOSCHI PIER MARINO, FUSCO RAFFAELLO, PISELLI FULVIO L, BOSCHI, PIER MARINO, FUSCO, RAFFAELLO, PISELLI, FULVIO L.
Applicants: PROFARMACO NOBEL SRL, PROFARMACO NOBEL S.R.L.
Application year: 1988
Main classification: C07D237
IPC codes: C07D491, C07D237