Process for the preparation of (2Z,5Z)-5-(3-chloro-4-((

1. A process for the preparation of (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde (1):

which process comprises reacting 3-chloro-4-hydroxybenzaldehyde with (R)-3-chloro-1,2-propanediol and isolating the obtained (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde by crystallisation.

2. The process according to claim 1 , wherein the reaction of 3-chloro-4-hydroxybenzaldehyde with (R)-3-chloro-1,2-propanediol is performed in the presence of the base potassium tert-butoxide and the solvent n-propanol, at elevated temperatures.

3. The process according to claim 1 , wherein the obtained (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde (1) is crystallised in water plus a co-solvent.

4. The process according to claim 3 , wherein the co-solvent is n-propanol.

5. The process according to claim 1 , further comprising reacting the obtained (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde (1) with 2-[(Z)-propylimino]-3-o-tolyl-thiazolidin-4-one to form (2Z,5Z)-5-(3-chloro-4-((R)-2,3-dihydroxypropoxy)benzylidene)-2-(propylimino)-3-(o-tolyl)thiazolidin-4-one (2):

6. The process according to claim 5 , wherein 2-[(Z)-propylimino]-3-o-tolyl-thiazolidin-4-one is prepared by reacting o-tolyl-iso-thiocyanate with n-propylamine followed by reaction with bromo-acetyl bromide and the base pyridine, wherein no isolation and/or purification of intermediates occurs and wherein the obtained 2-[(Z)-propylimino]-3-o-tolyl-thiazolidin-4-one is not isolated and/or purified before the reaction with (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde (1).

7. The process according to claim 6 , wherein (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde (1) is reacted with 2-[(Z)-propylimino]-3-o-tolyl-thiazolidin-4-one in the presence of the solvent ethanol and the base sodium acetate, at elevated temperatures.

8. The process according to claim 5 , characterised in that (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde (1) is isolated by a single crystallisation before the reaction with 2-[(Z)-propylimino]-3-o-tolyl-thiazolidin-4-one.

9. The process according to claim 5 , wherein in a first isolation step the obtained compound (2) is isolated by crystallisation.

10. The process according to claim 9 , wherein the compound (2) obtained after the first isolation step is in the crystalline form characterised by the presence of peaks in the X-ray powder diffraction diagram at the following angles of refraction 2θ: 10.5°, 11.1°, 11.4°, 13.6°, 13.9°, 16.3°, 20.8°, 22.2°, 23.4°, 24.1°, 25.7°, 27.7°, 27.9°, 28.7°, and 29.3°, wherein the X-ray powder diffraction diagram is obtained by using Cu Kα1 radiation (λ=1.5406 Å) and stripping of the Kα2 component and wherein the accuracy of the 2θ values is in the range of +/−0.2°.

11. The process according to claim 9 , wherein the obtained crystalline compound (2) is further purified by one or more recrystallisation steps.

12. The compound (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde in crystalline form.

13. The crystalline form according to claim 12 , characterised by the presence of peaks in the X-ray powder diffraction diagram at the following angles of refraction 2θ: 7.3°, 9.7°, 12.7°, 13.3°, 19.6°, 22.1°, 27.9°, and 28.5°, wherein the X-ray powder diffraction diagram is obtained by using Cu Kα1 radiation (λ=1.5406 Å) and stripping of the Kα2 component and wherein the accuracy of the 2θ values is in the range of +/−0.2°.

14. The crystalline form according to claim 12 , which has a melting point of about 94° C. as determined by differential scanning calorimetry.

15. A crystalline form of the compound (R)-3-chloro-4-(2,3-dihydroxypropoxy)-benzaldehyde obtainable by:

i) adding potassium tert-butoxide (118 g, 1.20 eq.) to n-propanol (963 mL) followed by 3-chloro-4-hydroxybenzaldehyde (137 g, 1.00 eq.);

ii) adding to the mixture (R)-3-chloro-1,2-propanediol (126 g, 1.30 eq.), heating the suspension to 90° C. and stirring it at this temperature for 17 h;

iii) distilling off the solvent (500 mL) at 120° C. external temperature and reduced pressure;

iv) adding water (1.1 L) and removing solvent (500 mL) by distillation;

v) cooling the turbid solution to 20° C. and stirring for one hour to obtain a white suspension;

vi) adding water (500 mL) and cooling the suspension to 10° C.;

vii) filtering the suspension and washing the resulting filter cake with water (500 mL); and

viii) drying the product at 50° C. and reduced pressure.

16. The crystalline form according to claim 15 , which has a melting point of about 94° C. as determined by differential scanning calorimetry.

17. A process for the preparation of (2Z,5Z)-5-(3-chloro-4-((R)-2,3-dihydroxypropoxy)benzylidene)-2-(propylimino)-3-(o-tolyl)thiazolidin-4-one comprising the process according to claim 1 .

18. The crystalline form according to claim 13 , which has a melting point of about 94° C. as determined by differential scanning calorimetry.