Process for the preparation of (1r,4r)-6′-fluoro-(N,N-dimethyl- and N-methyl)-4-phenyl-4′,9′-dihydro-3′H-spiro[cyclohexane-1,1′-pyrano-[3,4,b]indol]-4-amine

1. A process for preparing a compound corresponding to formula (I)

wherein R 1 represents H or CH 3 ,

or a physiologically acceptable acid addition salt thereof,

said process comprising:

(a) reacting a compound corresponding to formula (a-1) with a compound corresponding to formula (a-2), in each case optionally in the form of an acid addition salt, in the presence of at least one mono- or diprotic acid promoting agent,

wherein R 2 and R 3 in the compound of formula (a-2) together denote ═O, or together with the carbon atom connecting them form a cyclic moiety selected from the group consisting of

wherein R 4 and R 5 each independently represent 0, 1, 2, 3 or 4 substituents selected from the group consisting of H and CH 3 ,

in a carboxylic acid reaction medium to form the compound of formula (I).

2. The process according to claim 1 , wherein the compound of formula (I) is (1r,4r)-6′-fluoro-N,N-dimethyl-4-phenyl-4′,9′-dihydro-3′H-spiro[cyclohexane-1,1′-pyrano-[3,4b]indol]-4-amine having the formula:

or (1r,4r)-6′-fluoro-N-methyl-4-phenyl-4′,9′-dihydro-3′H-spiro[cyclohexane-1,1′-pyrano-[3,4b]indol]-4-amine having the formula:

or a physiologically acceptable acid addition salt thereof.

3. The process according to claim 1 , wherein the reaction medium comprises at least one carboxylic acid selected from the group consisting of formic acid, acetic acid, trifluoroacetic acid, propionic acid, lactic acid, 3-hydroxypropionic acid, butyric acid, isobutyric acid, acrylic acid, methacrylic acid, and mixtures of two or more of the foregoing.

4. The process according claim 3 , wherein the reaction medium comprises acetic acid or propionic acid or a mixture of acetic acid and propionic acid.

5. The process according to claim 1 , wherein the promoting agent is soluble in the reaction medium.

6. The process according to claim 1 , wherein the promoting agent is selected from the group consisting of inorganic acids and sulfonic acids.

7. The process according to claim 1 , wherein the promoting agent is selected from the group consisting of methanesulfonic acid, trifluoromethane sulfonic acid, p-toluenesulfonic acid, hexane-1-sulfonic acid, hydrochloric acid, hydrobromic acid, sulfuric acid, hydrogen sulfuric acid, hydrogen fluoride, hydrogen iodide, nitric acid, and sulfurous acid.

8. The process according to claim 1 , wherein the promoting agent is selected from the group consisting of hydrochloric acid, sulfuric acid, and trifluoromethane sulfonic acid.

9. The process according to claim 1 , wherein the compound of formula (I) is obtained in the form of an acid addition salt of said compound of formula (I) and said promoting agent.

10. The process according to claim 1 , wherein:

R 1 represents CH 3 , and

the promoting agent is selected from the group consisting of sulfuric acid and trifluoromethane sulfonic acid.

11. The process according to claim 1 , wherein:

R 1 represents H, and

the promoting agent is selected from the group consisting of hydrochloric acid, sulfuric acid and trifluoromethane sulfonic acid.

12. The process according to claim 1 , further comprising:

(b) converting a compound of formula (I) obtained from step (a) in the form of an acid addition salt with the promoting agent into the corresponding free base of formula (I).

13. The process according to claim 12 , wherein step (b) is carried out in a reaction medium in the presence of at least one base.

14. The process according to claim 13 , wherein:

said reaction medium selected from the group consisting of methanol, ethanol, isopropanol and mixtures of two or more of the foregoing, and

said base is selected from the group consisting of alkyl amines, dialkyl amines and trialkyl amines.

15. The process according to claim 12 , further comprising recrystallizing said free base of the compound of formula (I) obtained from step (b).