The condensation of 3-chloro-2,4,5-trifluorobenzoylacetic acid ethyl ester (I) with (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) and ethyl orthoformate (II) in hot acetic anhydride gives (1R,2S)-2-(3-chloro-2,4,5-trifluorobenzoyl)-3-(2-fluorocyclopropylamino)acrylic acid ethyl ester (IV). The cyclization of (IV) by means of NaH yields the quinolone (V), which is hydrolyzed with HCl to the free acid (VI). The condensation of (VI) with 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) by means of triethylamine in refluxing acetonitrile affords the protected final product (VIII), which is finally deprotected with trifluoroacetic acid and anisole.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) is obtained as follows: 1) The cyclization of butadiene (IX) with dibromofluoromethane by means of BuONa, followed by oxidation with KMnO4, esterification with ethanol - sulfuric acid and reduction with tributyltin hydride gives 2-fluorocyclopropanecarboxylic acid ethyl ester as a cis/trans mixture (X), which is separated by crystallization. The cis-racemic-isomer (XI) is hydrolyzed with NaOH to the corresponding acid (XII), which is condensed with (R)-alpha-methylbenzylamine (XIII) by means of diphenyl chlorophosphate to give the mixture of diastereomers (XIV). This mixture is separated by crystallization, yielding pure (1S,2S)-2-fluoro-N-[alpha(R)-methylbenzyl]cyclopropanecarboxamide (XV), which is hydrolyzed with HCl to the corresponding free acid (XVI). Finally, this compound is converted into (III) by treatment with diphenylphosphoryl azide in refluxing tert-butanol.

b) The intermediate 7(S)-(tert-Butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) can also be obtained as follows: 1) The cyclopropanation of ethyl acetoacetate (XXXI) with 1,2-dibromoethane (XXXII) by means of K2CO3 in DMF gives 1-acetylcyclopropane-1-carboxylic acid ethyl ester (XXXIII), which is brominated with Br2 in ethanol yielding the bromoacetyl derivative (XXXIV). The cyclization of (XXXI) with (R)-alpha-methylbenzylamine (XIII) by means of triethylamine affords 5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane-4,7-dione (XXXV), which by reaction with hydroxylamine is converted into the monooxime (XXXVI). The reduction of (XXXVI) with H2 over RaNi in methanol affords 7-amino-5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptan-4-one as a diastereomeric mixture (XXXVII) + (XXXVIII), which is separated by column chromatography. The reduction of the (7S)-isomer (XXXVIII) with LiAlH4 in THF gives 7(S)-amino-5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane (XXXIX), which is protected in the usual way to the tert-butoxycarbonyl derivative (XL). Finally, this compound is debenzylated to (VII) by hydrogenation with H2 over Pd/C in ethanol.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) is obtained as follows: 1) The cyclization of butadiene (IX) with dibromofluoromethane by means of BuONa, followed by oxidation with KMnO4, esterification with ethanol - sulfuric acid and reduction with tributyltin hydride gives 2-fluorocyclopropanecarboxylic acid ethyl ester as a cis/trans mixture (X), which is separated by crystallization. The cis-racemic-isomer (XI) is hydrolyzed with NaOH to the corresponding acid (XII), which is condensed with (R)-alpha-methylbenzylamine (XIII) by means of diphenyl chlorophosphate to give the mixture of diastereomers (XIV). This mixture is separated by crystallization, yielding pure (1S,2S)-2-fluoro-N-[alpha(R)-methylbenzyl]cyclopropanecarboxamide (XV), which is hydrolyzed with HCl to the corresponding free acid (XVI). Finally, this compound is converted into (III) by treatment with diphenylphosphoryl azide in refluxing tert-butanol.

b) The intermediate 7(S)-(tert-Butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) can also be obtained as follows: 2) The reaction of 1-acetylcyclopropane-1-carboxylic acid ethyl ester (XXXIII) with (R)-alpha-methylbenzylamine (XIII) by means of NaOH and ethyl chloroformate gives the corresponding amide (XLI), which by reaction with ethylene glycol and p-toluenesulfonic acid is converted into the ethylene ketal (XLII). The bromination of (XLII) with Br2 in dioxane affords the bromomethyl dioxolane (XLIII), which is finally cyclized to 5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane-4,7-dione (XXXV), already obtained as an intermediate in the preceding synthesis.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) can also be obtained as follows: 3) A study of the influence of different substituents in the cis/trans ratio of the cyclopropanation process has been performed. The general method is as follows: the reaction of benzylamine (XXIII) with acetaldehyde and trichloromethyl chloroformate gives the N-benzyl-N-vinylcarbamoyl chloride (XXIV), which by treatment with alcohol yields the N-vinylcarbamate (XXV). The cyclopropanation of (XXV) with fluorodiiodomethane and diethyl zinc as before preferentially affords the cis-N-(2-fluorocyclopropyl)carbamate (XXVI), which is purified by crystallization. The hydrogenolysis of (XXVI) with H2 over Pd/C in acetic acid gives cis-racemic-2-fluorocyclopropylamine (XXVII), which is submitted to optical resolution with L-menthyl chloroformate to afford pure (1R,2S)-isomer (XXII). Finally, this compound is converted into (III) with tert-butoxycarbonyl anhydride as before.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) can also be obtained as follows: 2) The cyclization of (1S,2R)-2-amino-1,2-diphenylethanol (XVII) with trichloromethyl chloroformate and triethylamine in dichloromethane gives (4R,5S)-4,5-diphenyloxazolidin-2-one (XVIII), which is treated with 1,1-dimethoxyethane and an acid catalyst, yielding the 1-methoxyethyl derivative (XIX). The heat treatment (150 C) of (XIX) affords the corresponding vinyl derivative (XX), which is cyclized with fluorodiiodomethane and diethyl zinc (a fluorocarbenoid compound) in a preferentially cis-way to afford the cyclopropyl-oxazolidinone (XXI), purified by column chromatography. The hydrogenolysis of (XXI) with H2 over Pd/C in acetic acid gives (1R,2S)-2-fluorocyclopropylamine (XXII), which is finally converted into (III) by reaction with tert-butoxycarbonyl anhydride and triethylamine in THF.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) can also be obtained as follows: 4) The cyclopropanation of 1-chloro-1-fluoroethylene (XXVIII) with diazoacetic esters (XXIX) catalyzed by rhodium catalysts, especially dirhodium (II) tetrakistriphenylacetate, gives preferentially the corresponding 2t-chloro-2c-fluorocyclopropane-1r-carboxylic esters (XXX), which are easily dechlorinated to the cis-racemic-2-fluorocyclopropanecarboxylic acid (XII), already obtained as intermediate in the synthesis shown in Scheme 2.

The condensation of 3-chloro-2,4,5-trifluorobenzoylacetic acid ethyl ester (I) with (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) and ethyl orthoformate (II) in hot acetic anhydride gives (1R,2S)-2-(3-chloro-2,4,5-trifluorobenzoyl)-3-(2-fluorocyclopropylamino)acrylic acid ethyl ester (IV). The cyclization of (IV) by means of NaH yields the quinolone (V), which is hydrolyzed with HCl to the free acid (VI). The condensation of (VI) with 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) by means of triethylamine in refluxing acetonitrile affords the protected final product (VIII), which is finally deprotected with trifluoroacetic acid and anisole.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) is obtained as follows: 1) The cyclization of butadiene (IX) with dibromofluoromethane by means of BuONa, followed by oxidation with KMnO4, esterification with ethanol - sulfuric acid and reduction with tributyltin hydride gives 2-fluorocyclopropanecarboxylic acid ethyl ester as a cis/trans mixture (X), which is separated by crystallization. The cis-racemic-isomer (XI) is hydrolyzed with NaOH to the corresponding acid (XII), which is condensed with (R)-alpha-methylbenzylamine (XIII) by means of diphenyl chlorophosphate to give the mixture of diastereomers (XIV). This mixture is separated by crystallization, yielding pure (1S,2S)-2-fluoro-N-[alpha(R)-methylbenzyl]cyclopropanecarboxamide (XV), which is hydrolyzed with HCl to the corresponding free acid (XVI). Finally, this compound is converted into (III) by treatment with diphenylphosphoryl azide in refluxing tert-butanol.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) can also be obtained as follows: 2) The cyclization of (1S,2R)-2-amino-1,2-diphenylethanol (XVII) with trichloromethyl chloroformate and triethylamine in dichloromethane gives (4R,5S)-4,5-diphenyloxazolidin-2-one (XVIII), which is treated with 1,1-dimethoxyethane and an acid catalyst, yielding the 1-methoxyethyl derivative (XIX). The heat treatment (150 C) of (XIX) affords the corresponding vinyl derivative (XX), which is cyclized with fluorodiiodomethane and diethyl zinc (a fluorocarbenoid compound) in a preferentially cis-way to afford the cyclopropyl-oxazolidinone (XXI), purified by column chromatography. The hydrogenolysis of (XXI) with H2 over Pd/C in acetic acid gives (1R,2S)-2-fluorocyclopropylamine (XXII), which is finally converted into (III) by reaction with tert-butoxycarbonyl anhydride and triethylamine in THF.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) can also be obtained as follows: 3) A study of the influence of different substituents in the cis/trans ratio of the cyclopropanation process has been performed. The general method is as follows: the reaction of benzylamine (XXIII) with acetaldehyde and trichloromethyl chloroformate gives the N-benzyl-N-vinylcarbamoyl chloride (XXIV), which by treatment with alcohol yields the N-vinylcarbamate (XXV). The cyclopropanation of (XXV) with fluorodiiodomethane and diethyl zinc as before preferentially affords the cis-N-(2-fluorocyclopropyl)carbamate (XXVI), which is purified by crystallization. The hydrogenolysis of (XXVI) with H2 over Pd/C in acetic acid gives cis-racemic-2-fluorocyclopropylamine (XXVII), which is submitted to optical resolution with L-menthyl chloroformate to afford pure (1R,2S)-isomer (XXII). Finally, this compound is converted into (III) with tert-butoxycarbonyl anhydride as before.

The chiral intermediate (1R,2S)-N-(tert-butoxycarbonyl)-2-fluorocyclopropylamine (III) can also be obtained as follows: 4) The cyclopropanation of 1-chloro-1-fluoroethylene (XXVIII) with diazoacetic esters (XXIX) catalyzed by rhodium catalysts, especially dirhodium (II) tetrakistriphenylacetate, gives preferentially the corresponding 2t-chloro-2c-fluorocyclopropane-1r-carboxylic esters (XXX), which are easily dechlorinated to the cis-racemic-2-fluorocyclopropanecarboxylic acid (XII), already obtained as intermediate in the synthesis shown in Scheme 2.

b) The intermediate 7(S)-(tert-Butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) can also be obtained as follows: 1) The cyclopropanation of ethyl acetoacetate (XXXI) with 1,2-dibromoethane (XXXII) by means of K2CO3 in DMF gives 1-acetylcyclopropane-1-carboxylic acid ethyl ester (XXXIII), which is brominated with Br2 in ethanol yielding the bromoacetyl derivative (XXXIV). The cyclization of (XXXI) with (R)-alpha-methylbenzylamine (XIII) by means of triethylamine affords 5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane-4,7-dione (XXXV), which by reaction with hydroxylamine is converted into the monooxime (XXXVI). The reduction of (XXXVI) with H2 over RaNi in methanol affords 7-amino-5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptan-4-one as a diastereomeric mixture (XXXVII) + (XXXVIII), which is separated by column chromatography. The reduction of the (7S)-isomer (XXXVIII) with LiAlH4 in THF gives 7(S)-amino-5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane (XXXIX), which is protected in the usual way to the tert-butoxycarbonyl derivative (XL). Finally, this compound is debenzylated to (VII) by hydrogenation with H2 over Pd/C in ethanol.

b) The intermediate 7(S)-(tert-Butoxycarbonylamino)-5-azaspiro[2.4]heptane (VII) can also be obtained as follows: 2) The reaction of 1-acetylcyclopropane-1-carboxylic acid ethyl ester (XXXIII) with (R)-alpha-methylbenzylamine (XIII) by means of NaOH and ethyl chloroformate gives the corresponding amide (XLI), which by reaction with ethylene glycol and p-toluenesulfonic acid is converted into the ethylene ketal (XLII). The bromination of (XLII) with Br2 in dioxane affords the bromomethyl dioxolane (XLIII), which is finally cyclized to 5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane-4,7-dione (XXXV), already obtained as an intermediate in the preceding synthesis.

A new synthesis of DU-6859 has been described: This compound is obtained by condensation of 8-chloro-6,7-difluoro-1-[2(S)-fluoro-1(R)-cyclopropyl]-4-oxo-1,4-dihydr oquinoline-3-carboxylic acid (I) with 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (II) by means of triethylamine in refluxing acetonitrile, followed by deprotection with 35% aqueous HCl. The starting compounds (I) and (II) are obtained as follows: 1) The reaction of (+/-)-cis-2-fluorocyclopropane-1-carboxylic acid (III) with 1(R)-phenylethylamine (IV) by means of N,N'-carbonyldiimidazole (CDI) gives the corresponding amide (V) as a mixture of diastereomers, which is submitted to preparative HPLC yielding 2(S)-fluorocyclopropane-1(R)-carboxylic acid 1(R)-phenylethylamide (VI). Hydrolysis of (VI) with hot 35% HCl affords the corresponding free acid (VII), which by reaction with diphenyl phosphorazidate in tert-butanol is converted to 1(R)-(tert-butoxycarbonylamino)-2(S)-fluorocyclopropane (VIII). The deprotection of (VIII) with trifluoroacetic acid gives the corresponding free amine as trifluoroacetate (IX), which is condensed with 2-(3-chloro-2,4,5-trifluorobenzoyl)-3-ethoxyacrylic acid ethyl ester (X) by means of triethylamine in dichloromethane to yield the chiral 3-aminoacrylate (XI). The cyclization of (XI) by means of NaH in dioxane affords 8-chloro-6,7-difluoro-1-[2(S)-fluoro-1(R)-cyclopropyl]-4-oxo-1,4-dihydroquinoline-3-carboxylic acid ethyl ester (XII), which is finally saponified to the desired acid (I) with hot 35% HCl.

2) The reaction of 1-acetylcyclopropane-1-carboxylic acid (XIII) with 1(R)-phenylethylamine (IV) by means of ethyl chloroformate and triethylamine gives the corresponding amide (XIV), which is treated with ethylene glycol and p-toluenesulfonic acid, yielding the dioxolane (XV). The bromination of (XV) with Br2 in dioxane affords the bromomethyl-dioxolane (XVI), which is cyclized by means of NaH in DMF to give 5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane-4,7-dione 7-ethyleneketal (XVII). Opening of the ketal ring with 1N HCl in refluxing acetone yields the free diketone (XVIII), which by reaction with hydroxylamine and triethylamine in ethanol affords the monooxime (XIX). The reduction of (XIX) with H2 over RaNi in methanol gives the aminoketone (XX) as a diastereomeric mixture, which is separated by column chromatography yielding 7(S)-amino-5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptan-4-one (XXI). The reduction of (XXI) with LiAlH4 in THF affords the amine (XXII), which is protected with 2-(tert-butoxycarbonyloxyimino)-2-phenylacetonitrile in THF to give 7(S)-(tert-butoxycarbonylamino)-5-[1(R)-phenylethyl]-5-azaspiro[2.4]heptane (XXIII). Finally, this compound is hydrogenolyzed with H2 over Pd/C in ethanol, yielding the desired chiral spiro compound (II).

An efficient synthesis of 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (XI), a key intermediate in the synthesis of DU-6859a, via an asymmetric microbial reduction has been described: The reaction of N-benzylglycine (I) with tert-butoxycarbonyl anhydride gives N-benzyl-N-(tert-butoxycarbonyl)glycine (II), which is condensed with the potassium salt of ethyl hydrogen malonate (III) by means of carbonyldiimidazole (CDI) in THF yielding 4-[N-benzyl-N-(tert-butoxycarbonyl)amino]-3-oxobutyric acid ethyl ester (IV). The cyclopropanation of (IV) with 1,2-dibromoethane (V) by means of K2CO3 in refluxing acetone affords the cyclopropane derivative (VI), which is cyclized by means of trifluoroacetic acid in dichloromethane to give 5-benzyl-5-azaspiro[2.4]heptane-4,7-dione (VII). The enantioselective microbial reduction of (VII) by means of Phaeocreopsis sp. JCM 1880 in a complex medium containing glucose and polypeptone yields 5-benzyl-7(R)-hydroxy-5-azaspiro[2.4]heptan-4-one (VIII), which by reaction with triphenylphosphine, diethyl azodicarboxylate and diphenylphosphoryl azide (DPPA) followed by reduction with LiAlH4, is converted into 7(S)-amino-5-benzyl-5-azaspiro[2.4]heptane (IX). The protection of (IX) with tert-butoxycarbonyl anhydride as usual gives the protected amine (X), which is finally debenzylated by hydrogenation with H2 over Pd/C in ethanol affording the desired 7(S)-(tert-butoxycarbonylamino)-5-azaspiro[2.4]heptane (XI).