Process for the preparation of polyhydroxystilbene compounds by deprotection of the corresponding ethers

1. A process for preparing polyhydroxy stilbenes of Formula I or its isomers thereof:

wherein

Rd, Rf, Ku and Rh are independently hydrogen or a OH group;

Ra, Rb, Re, and Re are independently a hydrogen, a halogen, a nitro group, a linear or branched C 1 -C 4 alkyl group, a linear or branched C 2 -C 6 alkenyl group, a C 3 -C 10 cycloalkyl group; a cycloalkylalkyl group in which the cycloalkyl is C 3 -C 10 cycloalkyl and the alkyl is C 1 -C 4 alkyl; an aryl group; or an aralkyl group;

the process comprising the step of deprotecting a compound of Formula II or its isomers thereof using an aluminum halide and a secondary amine

wherein

Ra, Rb, Rc and Re are defined as above;

Q is hydrogen or an OR i group; and

R 1 , R 2 and R i are independently a linear or branched C 1 -C 4 alkyl group; a C(═O)R j , wherein R j is a linear or branched C 1 -C 4 alkyl group; or an aralkyl group, wherein an aryl portion in the aralkyl group is optionally substituted by one or more C 1 -C 4 alkoxy or halogen groups.

2. The process of claim 1 , wherein Ra, Rb, Rc and Re are independently hydrogen, and one of Rd, Rf, Rg and Rh is hydrogen or a OH group.

3. The process of claim 1 , wherein Ra, Rb, Rc, and Re are independently hydrogen.

4. The process of claim 1 , wherein R 1 , R 2 and R i are independently a linear or branched C 1 -C 4 alkyl group; or an aralkyl group, wherein an aryl portion in the aralkyl group is optionally substituted by one or more C 1 -C 4 alkoxy or halogen groups.

5. The process of claim 4 , wherein R 1 , R 2 and R i are independently methyl, ethyl, t-butyl or benzyl group.

6. The process of claim 1 , wherein the aluminum halide is selected from the group consisting of aluminum chloride, aluminum bromide, and aluminum iodide.

7. The process of claim 6 , wherein the aluminum halide is aluminum chloride.

8. The process of claim 1 , wherein the secondary amine is of Formula (R) 2 NH, wherein R is a linear or branched alkyl group, a linear or branched C 2 -C 6 alkenyl group, a C 1 -C 6 alkanol, a C 3 -C 10 cycloalkyl group, a cycloalkylalkyl group, an aryl group, or an aralkyl group.

9. The process of claim 8 , wherein the secondary amine of Formula (R) 2 NH is selected from the group consisting of diemylamine, diisopropyl amine, di-n-propylamine, diisobutylarnine, diallylamine, allylmethyl amine, diphenylamine, dibenzylamine, benzylethyl amine, methylbenzyl amine, dicyclohexylamine, N-t-butyl cyclohexylamine, N-isobutyl cyclohexylamine, di(2-ethylhexyl)amine, and dicyclohexylmethyl amine.

10. The process of claim 8 , wherein the secondary amine of Formula (R) 2 NH is selected from the group comprising diisopropyl amine, diethylamine, di-n-propylamine, diisobutylarnine, dicyclohexylamine, and di(2-ethylhexyl)amine.

11. The process of claim 1 , wherein the deprotecting step is carried out in the presence of a solvent.

12. The process of claim 11 , wherein the solvent is a halogenated hydrocarbon selected from the group consisting of dichloromethane, dichloroethane, and chloroform; an aromatic hydrocarbon selected from the group consisting of toluene, xylene, chlorobenzene, and 1,2-dichlorobenzene; diphenyl ether; or mixtures thereof.

13. The process of claim 11 , wherein the solvent is toluene.

14. The process of claim 1 , wherein the deprotecting step is carried out at a temperature of ambient temperature to about reflux temperature.

15. The process of claim 14 , wherein the temperature is about 80° C. to about 120° C.

16. A process for preparing resveratrol of the formula

or its isomers thereof, the process comprising the step of deprotecting a resveratrol ether compound

or its isomers thereof,

wherein R 1 , R 2 and R 3 are independently a methyl, and

wherein the deprotecting step is carried out with use of an aluminum halide, and a secondary amine of Formula (R) 2 NH, wherein R is a linear or branched alkyl group, a linear or branched C 2 -C 6 alkenyl group, a C 1 -C 6 alkanol, a C 3 -C 10 cycloalkyl group, a cycloalkylalkyl group, an aryl group, or an aralkyl group.

17. The process of claim 16 , wherein the aluminum halide is aluminum chloride.

18. The process of claim 16 , wherein the secondary amine of Formula (R) 2 NH is selected from the group consisting of diisopropyl amine, diemylamine, di-n-propylamine, diisobutylamine, dicyclohexylamine, and di(2-ethylhexyl)amine.

19. The process of claim 16 , wherein the deprotecting step is carried out in the presence of a solvent.

20. The process of claim 19 , wherein the solvent is toluene.