Methods for the preparation of hexahydrofuro[2,3-B]furan-3-ol

1. A process for the preparation of a compound of formula (V) which comprises reacting 2,3-dihydrofuran of formula (II) with a glyoxylate derivative of formula (III) in the presence of a titanium salt of formula Ti(Hal) n (OR) 4-n in which Hal is a halogen radical, n is 0, 1, 2 or 3 and R is alkyl or arylalkyl, and subsequently reacting the resulting reaction product with an alcohol of formula (IV) to form a compound of formula (V):

in which R 1 is alkyl or arylalkyl and R 2 is alkyl or arylalkyl.

2. A process as claimed in claim 1 in which the titanium salt is a compound of formula Ti(Hal) n (OR) 4-n in which n is 1, 2 or 3.

3. A process as claimed in claim 1 in which R 1 is C 1-4 alkyl.

4. A process as claimed in claim 1 in which R 2 is C 1-4 alkyl.

5. A process as claimed in claim 1 in which 2,3-dihydrofuran of formula (II) is reacted with the glyoxylate derivative of formula (III) in the presence of the titanium salt and the subsequent reaction product is reacted with the alcohol of formula (IV) to form a compound of formula (V).

6. A process as claimed in claim 1 in which the resulting reaction mixture containing the compound of formula (V) is treated with Rochelle salt to effect removal of residual titanium compound.

7. A process as claimed in claim 6 in which the treatment with Rochelle salt is effected in an alkaline medium.

8. Compounds of formula (Va):

and the stereoisomeric forms and racemic mixtures thereof,

in which R 1 is alkyl or arylalkyl and R 2 is alkyl or arylalkyl, providing that when R 2 is methyl R 1 is not methyl or ethyl.

9. Ethyl hydroxy-(2-isopropoxytetrahydro-3-furanyl)acetate.

10. A process for the preparation of compounds of formula (VI) which comprises reducing a compound of formula (V) to form a compound of formula (VI):

in which R 1 and R 2 are as defined in claim 1 .

11. A process as claimed in claim 10 in which the reduction is effected with a borohydride reducing agent.

12. Compounds of formula (VI):

in which R 2 is as defined in claim 1 .

13. 1-(2-iso-Propoxytetrahydro-3-furanyl)-1,2-ethanediol.

14. A process for the preparation of a compound of formula (I) which comprises cyclising a compound of formula (VI) to form a compound of formula (I):

15. A process as claimed in claim 14 in which the cyclisation of the compound of formula (VI) is effected by treatment with a strong protic acid.

16. A process for the preparation of hexahydrofuro[2,3-b]furan-3-ol of formula (I) which comprises the stages of:

a) reacting 2,3-dihydrofuran of formula (II) with a glyoxylate derivative of formula (III) in the presence of a titanium salt of formula Ti(Hal) n (OR) 4-n in which n is 0, 1, 2 or 3 and R is alkyl or arylalkyl, and subsequently reacting the resulting reaction product with an alcohol of formula (IV) to form a compound of formula (V):

in which R 1 is alkyl or arylalkyl and R 2 is alkyl or arylalkyl; and

b) reducing the resulting compound of formula (V) to form a compound of formula (VI):

and

c) cyclising a compound of formula (VI) to form a compound of formula (I):

and if desired subsequently (i) subjecting the resulting compound of formula (I) to chiral separation to isolate (3R,3aS,6aR) hexahydrofuro-[2,3-b]furan-3-ol of formula (Ia):

and/or

(ii) oxidising the resulting compound of formula (I) to form a compound of formula (I′):

and subsequently reducing the compound of formula (I′) to a compound of formula (Ia).

17. A method of preparing [(1S,2R)-3-[[(4-Aminophenyl)sulfonyl](2-methylpropyl)amino]-2-hydroxy-1-(phenylmethyl)propyl]-carbamic acid (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yl ester comprising:

(a) preparing a hexahydrofuro[2,3-b]furan-3-ol of formula (I):

(3R,3aS,6aR) hexahydrofuro-[2,3-b]furan-3-ol of formula (Ia)

from a compound of formula (V) produced by the process of claim 1 :

in which R 1 is alkyl or arylalkyl and R 2 is alkyl or arylalkyl by reducing a compound of formula (V) to form a compound of formula (VI):

and cyclising the compound of formula (VI) to form a compound the formula (I) and optionally subjecting the resulting compound of formula (I) to chiral separation to isolate the compound of formula (Ia);

(b) reacting the compound of formula (I) or formula (Ia) with a coupling agent to generate a hexahydrofuro[2,3-b]furan-3-yl derivative; and

(c) carbamoylating said derivative with a compound of formula (5):

to form the [(1S,2R)-3-[[(4-Aminophenyl)sulfonyl](2-methylpropyl)amino]-2-hydroxy-1-(phenylmethyl)propyl]-carbamic acid (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yl ester.

18. The method of claim 17 wherein the coupling agent is a carbonate, chloroformate, phosgene or triphosgene.

19. A method of synthesizing [(1S,2R)-3-[[(4-Aminophenyl)sulfonyl](2-methylpropyl)amino]-2-hydroxy-1-(phenylmethyl)propyl]-carbamic acid (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yl ester comprising:

(a) preparing a hexahydrofuro[2,3-b]furan-3-ol of formula (I):

3aS,6aR) hexahydrofuro-[2,3-b]furan-3-ol of formula (Ia):

by the process of claim 16 ;

(b) reacting the compound of formula (I) or formula (Ia) with a coupling agent to generate a hexahydrofuro[2,3-b]furan-3-yl derivative; and

(c) carbamoylating said derivative with a compound of formula (5):

to form the [(1S,2R)-3-[[(4-Aminophenyl)sulfonyl](2-methylpropyl)amino]-2-hydroxy-1-(phenylmethyl)propyl]-carbamic acid (3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yl ester.

20. The method of claim 19 wherein the coupling agent is selected from the group consisting of bis-(4-nitrophenyl)carbonate, disuccinimidyl carbonate (DSC), carbonyl diimidazole (CDI), p-nitrophenylchloro-formate, phosgene and triphosgene.