WO2003035253A1

WO2003035253A1 - Process for the preparation of supported osmates

Info

Publication number: WO2003035253A1
Application number: PCT/IN2001/000187
Authority: WO
Inventors: Boyapati Manoranjan Choudary; Naidu Sreenivasa Chowdari; Mannepalli Lakshmi Kantam; Kondapuram Vijaya Raghavan
Original assignee: Council Of Scientific And Industrial Research
Priority date: 2001-10-23
Filing date: 2001-10-23
Publication date: 2003-05-01

Abstract

The present invention discloses a process for the preparation of a novel heterogeneous osmate catalyst of the general formula (S-NR3)2OsO4.nH2O wherein S is a support, R is an alkyl group, n is the number of water molecules by reacting potassium osmate with supported quaternary ammonium species in an aqueous solvent.

Description

PROCESS FOR THE PREPARATION OF SUPPORTED OSMATES Field of the invention

The present invention relates to a process for the preparation of supported osmates, which are useful as reusable catalysts in the preparation of vicinal diols. The present invention particularly relates to a process for the preparation of supported osmates of the formula (S-NR₃)₂OsO .nH₂O wherein S is a support, R is an alkyl group, n is the number of water molecules and use thereof in the preparation of vicinal diols by asymmetric dihydroxylation (AD) of olefins in presence of cinchona alkaloid compounds. Background of the invention The asymmetric dihydroxylation of olefins in the presence of cinchona alkaloid results in products that are important intermediates in the preparation of various drugs and chemicals. For example, the products of cinnamic acid esters are intermediates for taxol side chain, an anticancer drug, diltiazem, calcium antagonist and chloramphenicol, an antibiotic, proranolol, a β blocker can also be derived from diols obtained through this method. There are serious disadvantages in performing the catalytic AD reaction with homogeneous system in the manufacture of vicinal diols due to presence of toxic remnants of osmium in products and high cost of osmium 'tetraoxide or potassium osmate dihydrate. By employing the heterogeneous catalytic system, the cost naturally comes down due to easy recovery of the catalyst and very insignificant loss of osmium tetraoxide, when compared with homogeneous system. The products thus obtained using heterogeneous catalyst system are benign in the sense that the presence of osmium in minor impurities in the dihydroxylated products is also precluded,

US Patents 4,871.855 and 5,260,421 disclose a process for the asymmetric dihydroxylation of olefins using osmium tetraoxide and cinchona alkaloids using a homogenous catalyst system. These processes involve cumbersome recovery of the osmium catalyst from the reaction mixture, generation of toxic waste and the potential presence of toxic osmium in the product.

US Patent 5,516,929 discloses asymmetric dihydroxylation of olefins using osmium tetraoxide and polymer bound cinchona alkaloids in a heterogeneous system. The quantitative recovery of the toxic osmium catalyst, lower enantioselectivity and reduction in activity and enantioselectivity in each recycle experiments are some of the disadvantages associated with this process.

US Patent 5, 968,867 discloses the asymmetric dihydroxylation of olefins using • osmium tetraoxide and silica gel supported bis-cinchona alkaloid derivatives in a heterogeneous system. The quantitative recovery of the toxic osmium catalyst is difficult and a reduction in activity and enantioselectivity of the catalyst is observed in each and every recycle experiment.

European Patent 940,170 A2 describes the catalytic asymmetric dihydroxylation of alkenes using a polymer supported osmium catalyst. The drawbacks of this process are that higher amounts of catalyst are required (5 mol%), the reaction time is very long and expensive polymers are used as supports. Objects of the invention

The mam object of the invention is to provide a heterogeneous recyclable supported osmate of the general formula (S-NR₃)₂Osθ4.nH₂O wherein S is a support, R is an alkyl group, n is the number of water molecules and use thereof in the preparation of vicinal diols by asymmetric dihydroxylation (AD) of olefins in presence of cinchona alkaloid compounds.

It is another object of the invention to provide a process for the preparation of a novel heterogeneous recyclable supported osmate of the general formula (S-NR₃)₂OsO₄.ιιH₂θ wherein S is a support, R is an alkyl group, n is the number of water molecules and use thereof in the preparation of vicinal diols which process.

It is another object of the invention to provide a environmentally friendly process for the asymmetric dihydroxylation of olefins to obtain vicinal diols using a novel heterogeneous supported osmate of the invention. It is a further object of the invention to provide a process for the preparation of vicinal diols with good enantioselectivity, activity and yield by the asymmetric dihydroxylation of olefins using a novel osmate catalyst of the invention.

It is yet another object of the invention to provide a process for the preparation of vicinal diols by the asymmetric dihydroxylation of olefins in the presence of cinchona alkaloids and derivatives thereof, which process is simple, economical and results in a product with no traces of toxic osmium therein.

It is a further object of the invention to provide a process for the preparation of vicinal diols by the asymmetric dihydroxylation of olefins in the presence of cinchona alkaloids and derivatives thereof wherein the catalyst is capable of recycle several times without substantial loss of activity or in yield of product. Summary of the invention

These and other objects of the invention are achieved by using the novel supported heterogeneous osmate catalyst of the general formula (S-NR₃)₂OsO .nH₂O wherein S is a support, R is an alkyl group, n is the number of water molecules for the asymmetric dihydroxylation of olefins in the presence of cinchona alkaloids to obtain vicinal diols with good yield and selectivity.

The novelty of the invention lies in the supported osmate used as catalyst and in the preparation of vicinal diols in the presence of cinchona alkaloids or derivatives employing oxidants.

Accordingly, the present invention provides a supported osmate of the general formula (S-NR₃)₂θsθ₄. H₂O wherein S is a support, R is an alkyl group, n is the number of water molecules.

In one embodiment of the invention, the support is selected from resin or silica. In another embodiment of the invention, R is selected from methyl, ethyl, propyl, butyl and like alkyl groups.

In a further embodiment of the invention, the osmium content in the catalyst is in the range of 5 to 30%.

In a further embodiment of the invention, the support S used has charge balancing anions selected from chloride, bromide, iodide, fluoride, hydroxide and acetate.

The invention also relates to a process for the preparation of a novel heterogeneous osmate catalyst of the general formula (S-NR₃)2θsθ4,nH2θ wherein S is a support, R is an alkyl group, n is the number of water molecules, said process comprising reacting potassium osmate with supported quaternary ammonium species in an aqueous solvent at a temperature in the range of 20 to 30°C for a period in the range of 5 - 24 hours under nitrogen atmosphere followed by washing to obtain the desired catalyst.

In one embodiment of the invention, the osmium content in the catalyst is in the range of 5 to 30%.

In one embodiment of the invention, the support is selected from resin or silica.

In another embodiment of the invention, R is selected from methyl, ethyl, propyl, butyl and like alkyl groups.

The present invention also provides a process for the preparation of vicinal diols comprising asymmetrically dihydroxylating the corresponding olefin in the presence of a cinchona alkaloid using an oxidant such as herein described in a solvent system consisting of water and at least one of acetone, acetonitrile and t-butanoL in a ratio of water.aeetone, wateπacetonitrile and waterrt-butanol of 1:1 to 1:3, and water:acetone:acetonitrile in a ratio of 1 : 1 : 1 ; at a temperature in the range of -70 to 100°C for a period in the range of 0.5 to 24 hours, and in the presence of a catalytic amount of a heterogeneous supported osmate catalyst of the general formula (S-NR₃)₂OsO₄.nH₂O wherein S is a support, R is an alkyl group, n is the number of water molecules, and recovering the pure vicinal diol by any conventional method. In one embodiment of the invention, the osmium content in the catalyst is in the range of5 to 30%.

In yet another embodiment of the invention, the amount of supported osmate used in the reaction is 0.01 to 10 mol% of osmium content with respect to the substrate.

In another embodiment of the invention, the catalyst is recovered from the reaction system by any conventional process and recycled to the reaction system several times.

In a further embodiment of the invention, the oxidant used is selected from the group consisting of N-methylmorpholine N-oxide (NMO), trimethylamine N-oxide, hydrogen peroxide, t-butyl hydrogen peroxide, potassium ferricyanide, sodium periodate and molecular oxygen. In yet another embodiment of the invention, the cinchona alkaloid and derivatives thereof comprise a monomeric and polymeric chiral ligand.

In a further embodiment of the invention, the chiral ligand is selected from the group consisting of (DHQD)₂PHAL, (DHQD)₂PYR, (DHQD)₂AQN, DHQD-Oac, DHQD-CLB, DHQD-PHN, DHQD-MEQ, DHQD-IND and pseudoenantiomeric forms thereof. Detailed description of the invention

The novel supported osmate of the general formula (S-NR₃)₂OsO₄.nH₂O wherein S is a support, R is an alkyl group, n is the number of water molecules. The support is preferably selected from resin or silica. R is preferably selected from methyl, ethyl, propyl, butyl and like alkyl groups. The osmium content in the catalyst is generally in the range of 5 to 30%. The support S used may contain charge balancing anions selected from chloride, bromide, iodide, fluoride, hydroxide and acetate. The heterogeneous osmate catalyst of the general formula (S-NR₃)2θsO₄.nH₂O wherein S is a support, R is an alkyl group, n is the number of water molecules is prepared by reacting potassium osmate with supported quaternary ammonium species in an aqueous solvent at a temperature in the range of 20 to 30°C for a period in the range of 5 - 24 hours under nitrogen atmosphere followed by washing to obtain the desired catalyst.

The process for preparation of vicinal diols comprises asymmetrically dihydroxylating the corresponding olefin in the presence of a cinchona alkaloid using an oxidant in a solvent system consisting of water and at least one of acetone, acetonitrile and t- butanol, in a ratio of wateπacetone, water:acetonitrile and water:t-butanol of 1:1 to 1:3, and water:acetone:acetonitrile in a ratio of 1:1:1; at a temperature in the range of -70 to 100°C for a period in the range of 0.5 to 24 hours, and in the presence of a catalytic amount of a heterogeneous supported osmate catalyst of the general formula (S-NR₃)2θsO₄.nH₂θ where S is a support, R is an alkyl group, n is the number of water molecules, and recovering the pure vicinal diol by any conventional method. The amount of supported osmate used in the reaction is 0.01 to 10 mol% of osmium content with respect to the substrate.

The catalyst can be recovered from the reaction system by any conventional process and recycled to the reaction system several times without any substantial loss of activity or of yield of the product. The oxidant used is selected from N-methylmorpholine N-oxide (NMO), trimemylamine N-oxide, hydrogen peroxide, t-butyl hydrogen peroxide, potassium ferricyanide, sodium periodate and molecular oxygen. The cinchona alkaloid and derivatives thereof comprise a monomeric and polymeric chiral ligand such as for example (DHQD)₂PHAL, (DHQD)₂PYR, (DHQD)₂AQN, DHQD-OAc, DHQD-CLB, DHQD-PHN, DHQD-MEQ, DHQD-IND and pseudoenantiomeric forms thereof. Scientific explanation In the present invention, novel supported osmates were prepared for the first time using the anion exchange method from the supported quaternary ammonium species. The osmate anions present on the support are responsible for the dihydroxylation activity of the reaction. The activity of the supported osmate is similar or higher than the homogeneous counterparts. Without wishing to be bound by any theory, it is believed that the higher activity is ascribed to the support effect. The large positive potential of OsO42- support surface induces polarisation of N — O bond and facilitates oxygen transfer.

Higher yields and enantioselectivities are obtained with supported osmate catalysts used in the asymmetric dihydroxylation of olefins in aqueous organic solvents. Since the dihydroxylated products are important intermediates for the preparation of drugs and pharmaceuticals, this invention is timely and appropriate. Therefore, supported osmate is a better option for the synthesis of vicinol diols. The supported osmate catalysts prepared from various supports offered good yields and enantioselectivies in presence of cinchona alkaloids. Thus this invention offers the best techno-economic route for the synthesis of vicinol diols, intermediates for the preparation of drugs and pharmaceuticals.

Supported osmates are prepared as examplified and used in catalytic amounts for preparing vicinol diols by asymmetric dihydroxylation of olefins employing oxidants in presence of cinchona alkaloid compounds in a heterogeneous way as described in the examples. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the invention. Preparation of Catalysts

Example 1

Resin-Os0₄: Resin was obtained by quaternization of triethylamine (2.1 mL, 21 mmol) with 1 g of chloromethylated styrene-divinylbenzene copolymer (Merrifield resin, capacity ~2.1 mequiv/g) in chloroform (20 mL) under reflux for 24 h. 1 g of quaternary ammonium resin was suspended in 100 mL of 0.8 mmol aqueous potassium osmate solution and stirred at 25 °C for 12 h under nitrogen atmosphere. The solid catalyst was filtered, washed thoroughly with 300 mL of water and vacuum dried to obtain Resin-OsO₄ (0.641 mmol of Os per g).

Example 2 Siθ2-Os0₄: Modified silica was obtained by quaternisation of triethylamine (0.7 mL, 7 mmol) with bromopropylsilica (capacity 0.7 mequiv/g) in chloroform (20 mL) under reflux for 24 h. 1 g of quaternary ammonium silica was suspended in 100 mL of 0.33 mmol aqueous potassium osmate solution and stirred at 25 °C for 12 h under nitrogen atmosphere. The solid catalyst was filtered, washed thoroughly with 300 mL of water and vacuum dried to obtain SiO₂-OsO₄ (0.317 mmol of Os per g). Asymmetric Dihydroxylation of Olefins

The asymmetric dihydroxylation reaction of olefins was performed using the following method in order to evaluate supported osmates of the present invention.

Supported osmate (0.01 eq. wt. of osmium content), bis-cinchona alkaloid (DHQD)₂PHAL (0.01 Eq. Wt.) and N-methylmorpholine-N-oxide (1.5 Eq. Wt.) were stirred in the mixed solvent of water/acetone/acetonitrile (in the volume ratio of 1:1:1). To this mixture was added an olefin (1.0 Eq. Wt) slowly for a period of 12 h. After the reaction, the supported osmate catalyst was filtered off and washed with ethyl acetate. The combined filtrates were concentrated under reduced pressure. The chiral ligand was recovered from the aqueous layer after acidification (IN HC1). The concentrated organic layer was purified to afford the corresponding cis-diol by using conventional processes. The yield and the optical purity of the product were determined.

Catalytic asymmetric dihydroxylation of olefins using N-methylmorpholine-N-oxide as a co-oxidant

Example 3 Catalytic asymmetric dihydroxylation reaction of trans-stilbene by using Resin-OsO₄ : Resin-Osθ4 (0.01 Eq. Wt.), Hydroquinidine 1,4-phthalazinediyl diether

(DHQD)₂PHAL (0.01 Eq. Wt.) and N-methylmorpholine-N-oxide (1.5 Eq. Wt.) were stirred in the mixed solvent of water/acetone/acetonitrile (in the volume ratio of 1:1:1). To this mixture was added trans-stilbene (1.0 Eq. Wt) and stirred at room temperature for 6 hours. After the reaction, supported osmate catalyst was filtered off and washed with methanol. The combined filtrates were concentrated under reduced pressure. The chiral ligand was recovered from the aqueous layer after acidification (IN HC1). The pure product was obtained by removing the solvent at reduced pressure followed by column chromatography. (R,R)-(+)-l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 96%) [oc]_D +92.44 (c 1.0, EtOH): e.e.=99.4% Example 4

Catalytic asymmetric dihydroxylation reaction of trans-stilbene by using Resin-OsO₄ which had been used in Example 3 without further addition of osmate catalyst.

The reaction was performed using an identical process as in Example 3. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 95%) [cχ]_D +92.90 (c 1.0, EtOH): e.e.=99.9%

Example 5 Catalytic asymmetric dihydroxylation reaction of trans-stilbene by using Resin-OsO₄ which had been used in Example 4 without further addition of supported osmate catalyst.

The reaction was performed by using an identical process as in Example 3. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 97%) [c^χ:]_D +92.16 (c 1.0, EtOH): e.e.=99.1%

Example 6

Catalytic asymmetric dihydroxylation reaction of trans-stilbene by using Resin-OsO₄ which had been used in Example 5 without further addition of supported osmate catalyst. The reaction was performed by using an identical process as in Example 3. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 94%) [oc]_D +92.25 (c 1.0, EtOH): e.e.=99.2%

Example 7 Catalytic asymmetric dihydroxylation reaction of trans-stilbene by using Resin-Osθ4 which had been used in Example 6 without further addition of Supported osmate catalyst.

The reaction was performed by using an identical process as in Example 3. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 96%) [oc]_D +92.81 (c 1.0, EtOH): e.e.=99.8% Example 8

Catalytic asymmetric dihydroxylation reaction of trans-stilbene by using Resin-Osθ4 which had been used in Example 7 without further addition of supported osmate catalyst.

The reaction was performed by using an identical process as in Example 3. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 98%) [oc]_D +92.25 (c 1.0, EtOH): e.e.=99.2%

Example 9

Catalytic asymmetric dihydroxylation reaction of trans-stilbene by Siθ₂-OsO₄

The reaction was performed by using an identical process as in Example 3. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 97%) [ocj_D +92.34 (c 1.0, EtOH): e.e.=99,3%

Example 10

Catalytic asymmetric dihydroxylation reaction of styrene by using Resin-OsO₄

The reaction was performed by using an identical process as in Example 3 except slow addition of olefin with a reaction time of 12 hours. (R)-phenyl-l,2-ethanediol of more than 95.0% of enantiomeric excess was obtained (yield 94%) [o ]_D -34.29 (c 1.32, EtOH): e.e.=95.7%

Example 11 Catalytic asymmetric dihydroxylation reaction of trans-β-methyl styrene by using Resin- sO₄. The reaction was performed by using an identical process as in Example 3 except slow addition of olefin with a reaction time of 12 hours. (R,R)-l-phenyl-l,2-propanediol of more than 98.0% of enantiomeric excess was obtained (yield 97%) [oc]_D -30.50 (c 1.32, EtOH): e.e.=98.1% Example 12

Catalytic asymmetric dihydroxylation reaction of methyl trans-cinnamate by using Resin- OsO₄.

The reaction was performed by using an identical process as in Example 3 except slow addition of olefin with a reaction time of 12 hours. (2S,3R)-2,3-dihydroxy-3- phenylpropionate of more than 99% of enantiomeric excess was obtained (yield 96%) [oc]_D - 10.6 (c 1.0, CHC1₃): e.e.=99%

Example 13 Catalytic asymmetric dihydroxylation reaction of allyl 1-naphthyl ether by using Resin-OsO₄ The reaction was performed by using an identical process as in Example 3 except slow addition of olefin with a reaction time of 12 hours. 2,3-dihydroxypropyl- 1-naphthyl ether of more than 77.0% of enantiomeric excess was obtained (yield 94%) [oc]_D +5.18 (c 1.0, CH₃OH): e.e.=77.4%

Example 14 Catalytic dihydroxylation reaction of trans-stilbene by using Resin-OsO₄:

Resin-OsO₄ (0.01 Eq. Wt.), N-methyhnorpholine-N-oxide (1.5 Eq. Wt.) and trans- stilbene (1.0 Eq. Wt) in the mixed solvent of water/acetone/acetonitrile (in the volume ratio of 1:1:1) were stirred at room temperature for 6 hours. After completion of the reaction, the catalyst was filtered off and washed with ethyl acetate. The combined filtrates were concentrated under reduced pressure. The pure product, l,2-diphenyl-l,2-ethandiol was obtained by removing the solvent at reduced pressure followed by column chromatography. (yield 93%).

The experimental results in the Examples 3 to 14 were tabulated in Table 1&2.

Table 1. Reuse of Resin-Os0₄ for asymmetric dihydroxylation reaction of trans-stilbene

Εquivalent weight ratio of the reactants = olefin: osmium: cinchona alkaloid = 1:0.01:0.01, reaction temperature 25°C. ^b Yield percent after the separation by using column chromatography. ^c % e.e.(e.e. means enantiomeic excess) was determined by HPLC analysis using chiral columns ^dabsolute configuration was compared with the [ α ]_D values in the literature. Solvent Effects: Example 15

Catalytic asymmetric dihydroxylation reaction of trans-stilbene by Resin-OsO₄ :

The reaction was performed by an identical process as in Example 3 except the solvent is water/acetone (in the volume ratio of 1:3). (R,R)-(+)-l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 95%) [oc]_D +91.90 (c 1.0, EtOH): e.e.=99.0%

Example 16 Catalytic asymmetric dihydroxylation reaction of trans-stilbene by Resin-OsO₄ :

The reaction was performed by an identical process as in Example 3 except the solvent is water/acetonitrile (in the volume ratio of 1:3). (R,R)-(+)-l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 93%) [oc]_D +91.1 (c 1.0, EtOH): e.e.=99.0%

Example 17 Catalytic asymmetric dihydroxylation reaction of trans-stilbene by Resin-Osθ₄ :

The reaction was performed by an identical process as in Example 3 except the solvent is water/t-butanol (in the volume ratio of 1 :3) and the reaction time is 24 h. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 91%) [oc]_D +91.6 (c 1.0, EtOH): e.e.=99.0%

Example 18 Catalytic asymmetric dihydroxylation reaction of trans-stilbene by Resin-OsO₄ :

The reaction was performed by an identical process as in Example 3 except the solvent is water/t-butanol (in the volume ratio of 1:2) and the reaction time is 24 h. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 90%) [oc]_D+92.1 (c 1.0, EtOH): e.e.=99.0%

Example 19 Catalytic asymmetric dihydroxylation reaction of trans-stilbene by Resin-OsO₄ :

The reaction was performed by an identical process as in Example 3 except the solvent is water/t-butanol (in the volume ratio of 1 :1) and the reaction time is 36 h. (R,R)-(+)- l,2-diphenyl-l,2-ethandiol of more than 99.0% of enantiomeric excess was obtained (yield 92%) [oc]_D +92.3 (c 1.0, EtOH): e.e.=99.0%

Table 3. Solvent effects in catalytic asymmetric dihydroxylation reaction of trans- stilbene by Resin-Os0₄

The main advantages of the present invention are: 1. A novel and ecofriendly process for asymmetric dihydroxylation of olefins is presented.

2. The present process dispenses the use of soluble, toxic osmium tetraoxide or potassium osmate dihydrate instead heterogeneous reusable supported osmates are used.

3. Supported osmates are prepared and used for asymmetric dihydroxylation of olefins as heterogeneous catalysts. The use of heterogeneous supported osmates precludes the presence of osmium in traces with product.

4. The enantioselectivity and the yields are good.

5. The work-up procedure is simple.

6. The catalyst is subjected to many recycles, which displayed consistent activity.

7. The present process is environmentally safe since there is no disposal problem. 8. The process is economical.

Claims

We claim:

1. A process for the preparation of a novel heterogeneous osmate catalyst of the general formula (S-NR₃)₂θsθ₄.nH₂θ wherein S is a support, R is an alkyl group, n is the number of water molecules, said process comprising reacting potassium osmate with supported quaternary ammonium species in an aqueous solvent at a temperature in the range of 20 to 30°C for a period in the range of 5 - 24 hours under nitrogen atmosphere followed by washing to obtain the desired catalyst.

2. A process as claimed in claim 1 wherein the osmium content in the catalyst is in the range of 5 to 30%.

3. A process as claimed in claim 1 wherein the support S used has charge balancing anions selected from chloride, bromide, iodide, fluoride, hydroxide and acetate.

4. A process as claimed in claim 1 wherein the support is selected from resin or silica.

5. A process as claimed in claim 1 wherein R is selected from methyl, ethyl, propyl, butyl and like alkyl groups.

6. A process for the preparation of vicinal diols comprising asymmetrically dihydroxylating the corresponding olefin in the presence of a cinchona alkaloid using an oxidant such as herein described in a solvent system consisting of water and at least one of acetone, acetonitrile and t-butanol, in a ratio of wateπacetone, wateπacetonitrile and water:t- butanol of 1:1 to 1:3, and water:acetone:acetonitriIe in a ratio of 1:1:1; at a temperature in the range of -70 to 100°C for a period in the range of 0,5 to 24 hours, and in the presence of a catalytic amount of a heterogeneous supported osmate catalyst of the general formula (S-NR₃)₂Osθ₄.nH2θ wherein S is a support, R is an alkyl group, n is the number of water molecules, and recovering the pure vicinal diol by any conventional method.

7. A process as claimed in claim 6 wherein the osmium content in the catalyst is in the range of 5 to 30%.

8. A process as claimed in claim 6 wherein the support S used has charge balancing anions selected from chloride, bromide, iodide, fluoride, hydroxide and acetate.

9. A process as claimed in claim 6 wherein the support is selected from resin or silica.

10. A process as claimed in claim 6 wherein R is selected from methyl, ethyl, propyl, butyl and like alkyl groups.

11. A process as claimed in claim 6 wherein the amount of supported osmate used in the reaction is 0.01 to 10 mol% of osmium content with respect to the substrate.

12. A process as claimed in claim 6 wherein the catalyst is recovered from the reaction system by any conventional process and recycled to the reaction system several times.

13. A process as claimed in claim 6 wherein the oxidant used is selected from the group consisting of N-methylmorpholine N-oxide (NMO), trimethylamine N-oxide, hydrogen peroxide, t-butyl hydrogen peroxide, potassium ferricyanide, sodium periodate and molecular oxygen.

14. A process as claimed in claim 6 wherein the cinchona alkaloid and derivatives thereof comprise a monomeric and polymeric chiral ligand.

15. A process as claimed in claim 14 wherein the chiral ligand is selected from the group consisting of (DHQD)₂PHAL, (DHQD)2PYR, (DHQD)₂AQN, DHQD-OAc, DHQD- CLB, DHQD-PHN, DHQD-MEQ, DHQD-IND and pseudoenantiomeric forms thereof.