Sulphonylated diphenylethylenediamines, method for their preparation and use in transfer hydrogenation catalysis   

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application claiming priority to U.S. patent application Ser. No. 11/719,478, filed Jul. 17, 2007, now published as U.S. Patent Publication 2008/0081930 A1, and entitled “Sulphonylated Diphenylethylenediamines, Method for their Preparation and Use in Transfer Hydrogenation Catalysis.” The parent application, U.S. patent application Ser. No. 11/719,478, is a filing under 35 U.S.C. 371 of International Application No. PCT/GB2005/050190 filed Nov. 1, 2005, entitled “Sulphonylated Diphenylethylenediamines, Method for their Preparation and Use in Transfer Hydrogenation Catalysis,” claiming priority of United Kingdom Patent Application No. 0425320.9 filed Nov. 17, 2004. The above identified applications are incorporated by reference herein in their entirety.

Not Applicable.

Not Applicable.

This invention relates to diamines and in particular to substituted diphenylethylenediamines and catalysts derived therefrom. Such catalysts are useful for accelerating asymmetric hydrogenation reactions whose products are useful, for example, as chemical intermediates or reagents for use in the production of fine chemicals or pharmaceutical intermediates.

Catalytic asymmetric hydrogenation involves the activation of molecular hydrogen with chiral metal complexes. However, organic molecules can also be applied as the hydrogen donor in the presence of a suitable chiral catalyst in a process known as transfer hydrogenation. A hydrogen donor such as isopropanol or formic acid is conventionally used with catalysts of the type [(sulphonylated diamine)RuCI(arene)] for the reduction of carbonyl groups. This technology provides a powerful complement to catalytic asymmetric hydrogenation. Transfer hydrogenation, in fact, is particularly suitable for the asymmetric reduction of ketones that are difficult substrates for hydrogenation, such as acetylenic ketones and cyclic ketones.

Heretofore the sulphonylated diamine component of the transfer hydrogenation catalysts has been limited to sulphonylated diphenylethylenediamine (Dpen) and cycloalkyl-1,2-diamines such as 1,2-cyclohexane. For example transfer hydrogenation has been applied using [(tosyl-dpen)RuCI(arene)] catalysts to pharmaceutical products such as 10-hydroxy-dihydro-dibenz-[b,f]-azepines (see WO 2004/031155).

The sulphonylated diamine components used heretofore, while useful, are not equally effective across the range of desirable substrates. Thus, there is a need to expand the range of diamines suitable for use in transfer hydrogenation catalysts that provide catalysts of increased activity, selectivity or stability. We have recognised that, by introducing one or more substituting groups into the phenyl rings of diphenylethylenediamines and by variation of the sulphonate properties, the steric and electronic properties of the diamine component may be usefully adapted.

SUMMARY

Accordingly the present invention provides a diamine of formula (I)

in which A is hydrogen or a saturated or unsaturated C1-C20 alkyl group or an aryl group; B is a substituted or unsubstituted C1-C20 alkyl, cycloalkyl, alkaryl, alkaryl or aryl group or an alkylamino group and at least one of X1, X2, Y1, Y2 or Z is a C1-C10 alkyl, cycloalkyl, alkaryl, aralkyl or alkoxy substituting group.

The invention further provides a method for preparing a diamine of formula (I) comprising the steps of forming a substituted spiroimidazole from a substituted diketone of formula (II), where X1, X2, Y1, Y2 and Z are as above, reducing the substituted spiroimidazole to form a substituted diamine, optionally resolving the substituted diamine to an enantiomerically enriched form, and sulphonylating the substituted diamine.

The invention also provides a catalyst comprising the reaction product of a diamine of formula (I) and a suitable compound of a catalytically active metal.

DETAILED DESCRIPTION

In formula (I), A is hydrogen or a saturated or unsaturated C1-C20 alkyl group or an aryl group. The C1-C20 alkyl groups may be branched or linear, for example may be methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, hexyl, cyclohexyl, ethyl-hexyl, iso-octyl, n-nonyl, n-decyl, iso-decyl, tridecyl, octadecyl and isooctadecyl. The aryl group may be an unsubstituted or substituted phenyl, naphthyl or anthracylphenyl. Suitable substituting groups are hydroxy, halide (e.g. F, Cl, Br, I), C1-C20 alkoxy, amino, amido, nitrile and thiol. Preferably A is hydrogen, methyl ethyl, propyl or phenyl. Most preferably A is hydrogen.

In formula (I), B is introduced by sulphonylation of the optionally enantiomerically enriched substituted diamine. A wide range of sulphonylation compounds may be used to alter the properties of the sulphonylated diamine of formula (I). Accordingly, B may be a substituted or unsubstituted C1-C20 alkyl, cycloalkyl, alkaryl, alkaryl or aryl group, for example as described above, or an alkylamino group. By “alkylamino” we mean that B may be of formula —NR′12, where R′ is e.g. methyl, cyclohexyl or isopropyl or the nitrogen forms part of an alkyl ring structure. Fluoroalkyl or fluoroaryl groups may be used, for example B may be p-CF3—C6H4, C6F5 or CF2CF2CF2CF3 or CF3. Preferably B is an aryl group. The aryl group may be an unsubstituted or substituted phenyl, naphthyl or anthracylphenyl or heteroaryl compound such as pyridyl. Suitable substituting groups are C1-C20 alkyl as described above, trifluoromethyl, hydroxyl, halide (e.g. F, Cl, Br, I), C1-C20 alkoxy (especially methoxy), amino, amido, nitrile, nitro and thiol. Hence B may be for example o-Nitrophenyl, p-nitrophenyl, trichlorophenyl, trimethoxyphenyl, triisopropylphenyl, o-aminophenyl, benzyl (—CH2C6H5), 2-phenylethyl(C2H4C6H5), phenyl(C6H5), tolyl(p-CH3—C6H4), xylyl((CH3)2C6H3), anisyl(CH3O—C6H4), naphthyl or dansyl (5-dimethylamino-1-naphthyl). Preferably, B is tolyl and the sulphonylation is performed with tosyl chloride (p-toluenesulphonyl chloride).

The diamine of the present invention has two chiral centres, each bearing a phenyl ring having at least one substituting group X1, X2, Y1, Y2 or Z. The substituting group X1, X2, Y1, Y2 or Z is a C1-C10 alkyl, cycloalkyl, alkaryl, aralkyl or alkoxy group. It will be understood that in order to satisfy the valency of the carbon atoms in the phenyl rings to which X1, X2, Y1, Y2 or Z is bound, where X1, X2, Y1, Y2 or Z is not a C1-C10 alkyl, cycloalkyl, alkaryl, aralkyl or alkoxy substituting group, X1, X2, Y1, Y2 or Z will be a hydrogen atom.

Thus at least one of X1, X2, Y1, Y2 or Z may independently be a C1-C10 alkyl group such as methyl, trifluoromethyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, ethyl-hexyl, iso-octyl, n-nonyl, n-decyl or iso-decyl; an alkaryl group such as benzyl or ethylphenyl; an aryl group such as phenyl, tolyl or xylyl; or a C1-C10 alkoxy group such as methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, iso-butoxy, sec-butoxy, tert-butoxy, cyclopentoxy, pentoxy, hexoxy, cyclohexoxy, ethyl-hexoxy, iso-octoxy, n-nonoxy, n-decoxy or iso-decoxy.

Preferably each phenyl ring has one or more substituents. The phenyl rings may be substituted in one or more positions, i.e. the rings may be mono-, di-, tri-, tetra- or penta-substituted. The substituting group on the phenyl ring may be in the ortho (X1, X2), meta (Y1, Y2) or para (Z) position. However, when the substituent is at the mete-position of the phenyl ring it minimizes the electronic effects on the amino group, which may facilitate the synthesis of the resulting diamine. Thus one embodiment the substituted diamine is a 1,2-di-(meta-substituted phenyl)ethylenediamine. Where more that one substituting group is present they are preferably the same. For example in one embodiment, Y1, Y2 may be hydrogen and X1, X2 and Z are preferably the same alkyl, cycloalkyl, alkaryl, aralkyl or alkoxy substituting group. In an alternative embodiment X1, X2 and Z may be hydrogen and Y1 and Y2 are preferably the same alkyl, cycloalkyl, alkaryl, aralkyl or alkoxy substituting group. In a preferred embodiment X1, X2, Y1 and Y2 are hydrogen and Z is a C1-C10 alkyl, cycloalkyl, alkaryl, aralkyl or alkoxy substituting group. In a particularly preferred embodiment, X1, X2, Y1 and Y2 are hydrogen and Z is methyl. In another particularly preferred embodiment, X1, X2, Y1 and Y2 are hydrogen and Z is methoxy.

The substituted diamines of the present invention may be conveniently made from substituted diketones of formula (II) where X1, X2, Y1, Y2 and Z are as above, via a spiro-imidazole, which is then reduced to a diamine and sulphonylated.

Substituted diketones (benzils) of formula (II) can be obtained commercially or can be readily prepared from substituted benzaldehydes of formula (III) where X1, X2, Y1, Y2 and Z are as above, by benzoin condensation followed by oxidation of the resulting substituted benzoin. Substituted benzaldehydes are commercially available or may be synthesised using known substitution reactions. Benzoin condensation reactions are well known and are typically performed by reacting a substituted benzaldehyde in a suitable solvent in the presence of sodium cyanide (see for example Ide et al, Org. React. 1948, 4, 269-304). The oxidation of the substituted benzoin to the diketone may readily be performed using copper acetate and ammonium nitrate (for example see Weiss et al, J. Am. Chem. Soc, 1948, 3666).

The spiroimidazole may be formed by treating the substituted diketone of formula (II) with acetic acid, ammonium acetate and cyclohexanone and heating to reflux. The reduction of the resulting substituted benzoin to the substituted diamine may be performed by mixing a solution of the spiroimidazole with lithium wire and liquid ammonia at below −60° C., treating the mixture with ethanol and ammonium chloride and allowing the mixture to warm to room temperature. The substituted diamine is sulphonylated to provide the substituted diamines of the present invention.

The substituted diamine may then be sulphonylated by treating the substituted diamine in a suitable solvent with the desired sulphonyl chloride, i.e. Cl—SO2—B, and a base such as triethylamine.

The nitrogen atoms in the substituted diamine are bonded to chiral centres and so the substituted diamine is chiral. The diamine may be homochiral, i.e. (R,R) or (S,S), or have one (R) and one (S) centre. Preferably the diamine is homochiral. Whereas the diamine may be used as a racemic mixture, the amine is preferably enantiomerically enriched. The resolution of the chiral substituted diamine may be performed using a chiral acid or by any other method known to those skilled in the art. Whereas the resolution may be performed on the sulphonylated diamine of formula (I), preferably the resolution is performed on the substituted diamine before the sulphonylation step. For example, the substituted diamine may be treated with a chiral carboxylic acid such as ditoluoyltartaric acid or dibenzoyltartaric acid in a suitable solvent. The resolved substituted diamine preferably has an enantiomeric excess (ee %)>70%, more preferably >90%.

Hence this route provides an efficient and cost effective method to prepare enantiomerically enriched substituted 1,2-diphenylethylenediamines. The route is depicted below for a preferred example where A, X1, X2, Y1 and Y2 are hydrogen, B is e.g. p-CH3—C6H5 and Z is a C1-C10 alkyl, cycloalkyl, alkaryl, aralkyl or alkoxy substituting group;

Catalysts suitable for performing asymmetric transfer hydrogenation reactions may be prepared by reacting the substituted sulphonylated diamines of the present invention with a suitable compound of a catalytically active metal. The metal compound is preferably a compound of metals selected from the list consisting of Ru, Rh, Ir, Co, Ni, Fe, Pd or Pt. Preferred compounds are compounds of Ru, Rh and Ir, particularly Ru or Rh. Suitable Ru or Rh compounds are [MX2(arene)]2 compounds where M=Rh or Ru and X=halogen, more preferably [RuCl2(arene)]2. Arene compounds are any suitable aromatic molecule, and include benzenes and cyclopentadienes, e.g. benzene, pentamethylcylcopentadiene and para-cymene (4-isopropyltoluene). Particularly suitable metal compounds for preparing hydrogenation catalysts include [RhCp*Cl2]2 (where Cp* is CpMe5), [RuCl2(benzene)]2 and [RuCl2(p-cymene)]2.

The catalysts may be prepared by simply combining the diamine and the metal compound in a suitable solvent under mild conditions (e.g. 0 to 80° C. at about atmospheric pressure). Suitable solvents include hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, esters, alcohols, ethers, DMF and the like. If desired, the reaction may be performed ex-situ and the resulting catalyst isolated, e.g. by removal of the solvent under vacuum. Alternatively, the catalyst may be formed in-situ, i.e. in the presence of the substrate to be hydrogenated and the hydrogen source, again by combining the metal compound and diamine in the reactants, which may be diluted with a suitable solvent.

The chiral catalysts of the present invention may be applied to transfer hydrogenation reactions. Typically, a carbonyl compound or imine, hydrogen source, base and solvent are mixed in the presence of the catalyst, which may be formed in-situ. Preferred hydrogen sources are isopropanol or formic acid (or formates). The catalysts may be used to reduce a wide variety of carbonyl compounds to the corresponding chiral alcohols and imines to the corresponding chiral amines. The reactions may be carried out under typical transfer hydrogenation conditions and in a variety of suitable solvents known to those skilled in the art. For example, the reaction may be performed in an ether, ester or dimethylformamide (DMF) at 0-75° C. Water may be present. With formic acid, a base such as triethylamine, DBU or other tertiary amine is preferably used. With isopropanol, the base is preferably t-BuOK, KOH or iPrOK.

The invention is illustrated by the following examples.

(I) Spiro-Imidazole Formation (1 to 2)

a) Z=Methyl(CH3): Acetic acid (70 ml) was added to a flask containing the commercially available diketone 1a (dimethylbenzyl 11.9 g, 50 mmol) and ammonium acetate (27 g, 350 mmol). Cyclohexanone (5.3 ml, 51.5 mmol) was added and the reaction mixture was heated at reflux for 1-4 hours. After cooling to room temperature, the mixture was poured onto water and left overnight to crystallize. The crystals were collected by filtration and dried under reduced pressure. Recrystallization was from ethyl acetate/hexane and gave 8.22 and 3.32 g of 2a in 2 crops. Total yield 11.54 g, 73%.

b) Z=Methoxy(CH3O): Acetic acid (100 ml) was added to a flask containing the commercially available diketone 1b (dimethoxybenzil, 18.9 g, 70 mmol) and ammonium acetate (37.7 g, 490 mmol). Cyclohexanone (7.45 ml, 72.1 mmol) was added and the reaction mixture was heated at reflux for 1-4 hours. After cooling to room temperature, the mixture was poured onto water and left overnight to crystallize. The crystals were collected by filtration and dried under reduced pressure. Yield of imidazole 2b, 19.22 g, 79%. Further purification can be achieved by crystallisation from ethyl acetate/hexane.

(II) Reduction (2 to 3)

a) Z=Methyl(CH3): Ammonia gas was slowly condensed into a solution of the spiro-imidazole 2a (6.95 g, 22 mmol) in anhydrous THF (50 ml) at −78° C. under argon. Once the volume of the reaction mixture has approximately doubled, the gas flow was stopped. Lithium wire (0.62 g, 88 mmol) was added slowly ensuring that the temperature did not exceed −60° C. After stirring for 30-60 minutes ethanol (2.6 ml) was added, and 30-60 minutes later ammonium chloride (6.2 g) was added. The mixture was allowed to warm to room temperature and water (about 100 ml) and MTBE (about 100 ml) were added. The layers were separated and the aqueous layer was extracted twice with about 100 ml MTBE. The combined organic layers were washed with brine and evaporated under vacuum. The resulting oil was dissolved in MTBE and 10% HCl was added (2-3 eq.). The biphasic mixture was stirred for 30-90 minutes and was diluted with water. The layers were separated and the organic layer was extracted with water. The combined aqueous layers were washed with dichloromethane and then neutralised with aqueous KOH until the pH>10. The crude diamine was extracted into dichloromethane (3 times). The combined organic extracts dried (Na2SO4) and evaporated to give an oil or solid. Yield of racemic diamine 3a as a 19:1 mixture of diastereoisomers, 4.96 g, 94%. Further purification can be achieved by crystallisation from ethyl acetate/hexane.

b) Z=Methoxy(CH3): Ammonia gas was slowly condensed into a solution of the spiro-imidazole 2b (6.96 g, 20 mmol) in anhydrous THF (40 ml) at −78° C. under argon. Once the volume of the reaction mixture has approximately doubled, the gas flow was stopped. Lithium wire (0.56 g, 80 mmol) was added slowly ensuring that the temperature did not exceed −60° C. After stirring for 30-60 minutes ethanol (2.4 ml) was added, and 30-60 minutes later ammonium chloride (2.8 g) was added. The mixture was allowed to warm to room temperature and water (about 100 ml) and MTBE (about 100 ml) were added. The layers were separated and the aqueous layer was extracted twice with about 100 ml MTBE. The combined organic layers were washed with brine and evaporated under vacuum: The resulting oil was dissolved in MTBE and 10% HCl was added (2-3 eq.). The biphasic mixture was stirred for 30-90 minutes and was diluted with water. The layers were separated and the organic layer was extracted with water. The combined aqueous layers were washed with dichloromethane and then neutralised with aqueous KOH until the pH>10. The crude diamine was extracted into dichloromethane (3 times). The combined organic extracts dried (Na2SO4) and evaporated to give an oil or solid. Yield of racemic diamine 3b as a 19:1 mixture of diastereoisomers, 4.69 g, 86%. Further purification can be achieved by crystallisation from ethyl acetate/hexane.

(III) Chiral Resolution of Diamines

a) Resolution of diamine 3a. Formation of a salt with ditoluoyltartaric acid in methanol and crystallisation from methanol initially gave (R,R) 4a in 94% ee. This can be increased to >99% with one further crystallisation.

b) Resolution of diamine 3b. Formation of a salt with ditoluoyltartaric acid in methanol and crystallisation from methanol initially gave (S,S) 4b in 74% ee. It should be possible to increase the ee by further crystallisation. Formation of a salt with dibenzoyltartaric acid in methanol and crystallisation from methanol initially gave 4b in 98% ee.

(IV) Synthesis of Mono-Sulfonylated Diamines

a) Tosyl-5a (Z=CH3, B=4-CH3—C6H4). Triethylamine (210 μl, 1.5 mmol) was added to a solution of the diamine 4a (180 mg, 0.75 mmol) in anhydrous dichloromethane (8 ml) and the solution was cooled to 0° C. A solution of the tosyl chloride (p-toluenesulphonyl chloride, 148 mg, 0.77 mmol) in anhydrous dichloromethane (4 ml) was added slowly. The mixture was stirred at 0° C. for 30-120 minutes and allowed to warm to room temperature over 1-24 hours. Water was added and the layers separated. The aqueous layer was extracted twice with dichloromethane and the combined organic layers were washed with brine, dried (Na2SO4) and evaporated. The crude mono-sulfonated diamine could be purified by column chromatography. Purification by column chromatography gave 270 mg (91%) of Ts-5a as a white solid.

b) Tosyl-5b (Z=OCH3, B=4-CH3—C6H4). Triethylamine (190 μl, 1.3 mmol) was added to a solution of the diamine 4b (175 mg, 0.65 mmol) in anhydrous dichloromethane (8 ml) and the solution was cooled to 0° C. A solution of the tosyl chloride (p-toluenesulphonyl chloride, 1428 mg, 0.67 mmol) in anhydrous dichloromethane (5 ml) was added slowly. The mixture was stirred at 0° C. for 30-120 minutes and allowed to warm to room temperature over 1-24 hours. Water was added and the layers separated. The aqueous layer was extracted twice with dichloromethane and the combined organic layers were washed with brine, dried (Na2SO4) and evaporated. The crude mono-sulfonylated diamine could be purified by column chromatography. Purification by column chromatography gave 270 mg (91%) of Ts-5b as a white solid.

A mixture of [Ru(p-cymene)Cl2]2 (0.5 eq.), triethylamine (2 eq.), mono-sulfonated diamine (1 eq.) 5b in anhydrous isopropanol was heated at 70-90° C. for 1-4 hours under an inert atmosphere. After cooling to room temperature the solution was concentrated under reduced pressure and the orange solid collected by filtration. The solid was washed with degassed water and a small amount of methanol then further dried under reduced pressure. Further purification can be performed by precipitation/crystallisation from hot methanol.

Transfer hydrogenation catalysts bearing diamines 5 were prepared in situ and tested on pre-formed mixture of ketones in DMF. [Ru(p-cymene)Cl2]2 (0.0025 mmol) or [RhCp*Cl2]2 (0.0025 mmol) mono-sulfonated diamine (0.0055 mmol) 5 in anhydrous DMF (2 mL) were heated at 40° C. for 10 minutes under inert atmosphere (argon). A solution of five ketones (0.5 mL, 1 mmol in total, 0.2 mmol each) in DMF was added (S/C 40 with respect to each substrate), followed by 0.6 mL of formic acid/trietylamine 1/1 mixture and 1 mL of DMF. The reaction was heated overnight (20 hrs) at 60° C. and analysed by CG (ChiraDex CB column, 10 psi He, 100° C. for 12 min, then to 180° C. at 1.5° C./min, then to 200° C. at 5° C./min).

For reference, the diamines tested were as follows:

5b, (S,S)-TsDAEN 5a,(R,R)-TsDTEN (S,S)-TsDPEN Ketone (S,S)-Ts-DAEN-Ru >95% conv 33% conv >95% conv >95% conv >95% conv S/C 100/1 55% ee 40% ee 96% ee 29% ee 92% ee (S,S)-Ts-DAEN-Ru >95% conv 10% conv >95% conv >95% conv >95% conv S/C 200/1 57% ee 42% ee 98% ee 27% ee 94% ee (R,R)-Ts-DTEN-Ru >95% conv 11% conv >95% conv >95% conv >95% conv S/C 200/1 53% ee 35% ee 96% ee 28% ee 91% ee (S,S)-Ts-DAEN-Ru >95% conv 48% conv  51% conv >95% conv  47% conv S/C 100/1 72% ee 13% ee 98% ee 13% ee 90% ee conv = conversion ee enantlomeric excess