Method for the preparation of hexahydro-furo-[2,3-b]furan-3-ol

1. A method for the synthesis of hexahydro-furo[2,3-b]furan-3-ol of formula (7) starting from an intermediate of formula (1) wherein P 1 and P 2 represent each independently a hydrogen, a hydroxy-protecting group or may together form a vicinal-diol protecting group,

transforming said intermediate of formula (1) into a nitromethane derivative of formula (3) wherein R 1 represents alkyl, aryl or aralkyl, R 2 represents hydrogen or C(═O)OR 3 , R 3 represents alkyl, aryl or aralkyl, or R 3 , if present, and R 1 taken together with the atoms to which they are attached may form a 6 to 8-membered cyclic group which may be optionally substituted with alkyl, aralkyl, or aryl,

subsequently transforming said nitromethane derivative into a tetrahydrofuran derivative of formula (6) wherein OR 4 represents an alcoholate,

and then transforming the intermediate of formula (6) into hexahydro-furo[2,3-b]furan-3-ol of formula (7) by way of an intramolecular cyclisation reaction

2. A method according to claim 1 wherein the intermediate of formula (3) is transformed into an intermediate of formula (6) by making use of a Nef reaction.

3. A method according to claim 1 for the synthesis of hexahydro-furo[2,3-b]-furan-3-ol of formula (7), which comprises the steps of:

a) condensing an intermediate of formula (1)

 resulting in an α,β-unsaturated ester of formula (2),

b) reacting said ester of formula (2) with nitromethane resulting in an intermediate of formula (3),

c) submitting said intermediate of formula (3) to a Nef reaction leading to intermediates of formula (4) and (4′)

d) transforming said intermediates of formula (4) and (4′) into an intermediate of formula (6) and,

e) converting intermediate of formula (6) to the compound of formula (7) by an intramolecular cyclisation reaction.

4. A method according to claim 1 for the synthesis of hexahydro-furo[2,3-b]furan-3-ol of formula (7), which comprises the steps of:

a) condensing an intermediate of formula (1) with CHR 2 R 5 —C(═O)—OR 1 wherein R 5 represents a hydrogen, a carboxylic ester, a phosphonium salt or a phosphonate ester,

 resulting in an α,β-unsaturated ester of formula (2)

b) reacting said ester of formula (2) with nitromethane resulting in an intermediate of formula (3),

c) submitting said intermediate of formula (3) to a Nef reaction by treating it with a base and subsequently with a strong acid resulting in a mixture of intermediates of formula (4) and (4′),

d) only in case R 2 is different from hydrogen, decarboxylating the intermediates of formula (4) and (4′) thus forming intermediates of formula (5) and (5′) respectively,

e) reducing intermediates of formula (4) and (4′), or intermediates of formula (5) and (5′) with a suitable reducing agent resulting in intermediate of formula (6) and,

f) converting intermediate of formula (6) to the compound of formula (7) by an intramolecular cyclisation reaction.

5. A method according to claim 1 for the synthesis of hexahydro-furo[2,3b]furan-3-ol of formula (7.1) starting from an intermediate of formula (1), wherein P 1 and P 2 taken together form an isopropylidene,

condensing said intermediate of formula (1) resulting in an intermediate of formula (2), wherein P 1 and P 2 taken together form an isopropylidene, R 2 represents —C(═O)OR 3 , wherein R 3 is methyl and R 1 is methyl,

reacting said ester of formula (2) into a nitromethane derivative of formula (3) wherein P 1 and P 2 taken together form an isopropylidene, R 2 represents —C(═O)OR 3 , wherein R 3 is methyl, and R 1 is methyl,

transforming said intermediate of formula (3) using a base and subsequently an acid to yield intermediates of formula (4) and (4′), wherein R 2 represents —C(═O)OR 3 , wherein R 3 is methyl, R 1 is methyl and R 4 is methyl,

decarboxylating intermediates of formula (4) leading to an intermediate of formula (5), wherein R 4 is methyl,

reducing said intermediate of formula (5) with a suitable reducing agent resulting in an intermediate of formula (6), wherein R 4 is methyl,

transforming the intermediate of formula (6) into compound 7.1 by way of intramolecular cyclization reaction

6. A method according to claim 3 wherein intermediate of formula (3) is submitted to a Nef reaction using acidic quenching while keeping the temperature below −10° C. during said quenching.

7. A method according to claim 4 wherein the decarboxylation of intermediates of formula (4) and (4′) is performed in a buffered aqueous solution.

8. A method according to claim 3 wherein intermediate (6) is prepared via reduction of intermediates of formula (4) and (4′) or intermediates of formula (5) and (5′) using lithium borohydride in tetrahydrofuran or NaBH 4 in the presence of LiCl.

9. A method according to claim 3 wherein the cyclisation of intermediate of formula (6) to the compound of formula (7) is performed by adding a strong acid to the reaction mixture containing intermediate of formula (6).

10. A method according to claim 9 wherein the cyclisation reaction is performed at a temperature lower then 5° C.

11. A method according to claim 10 wherein the temperature of the reaction mixture while adding the strong acid to the reaction mixture remains lower than −5° C.

12. A method according to claim 1 wherein an intermediate of formula (3) is prepared by a process comprising the steps of first condensing an intermediate of formula (1) with nitromethane, resulting in an intermediate of formula (8) and secondly, reacting said intermediate of formula (8) with CHR 2 R 8 —C(═O)—OR 1 wherein R 8 is hydrogen or a carboxylic ester

13. A method according to claim 12 wherein the carboxylic ester is defined as C(═O)—OR 1 .

14. A method according to claim 1 wherein an intermediate of formula (6) is prepared by a process comprising the steps of first reducing intermediate of formula (3) wherein R 2 is hydrogen with a suitable reducing agent, resulting in an intermediate of formula (9) and secondly submitting the obtained intermediate of formula (9) to a Nef reaction by treatment with a base and then with a strong acid

15. A method according to claim 1 wherein hexahydro-furo[2,3-b]furan-3-ol of formula (7) is isolated by adding a small excess of a tertiary amine, followed by the removal of water and removal of formed salts.

16. A method according to claim 1 wherein R 1 and R 3 each independently are C 1-6 alkyl, aryl or arylC 1-6 alkyl or together with the atoms to which R 1 and R 3 are attached form a 6 to 8-membered cyclic group optionally substituted with C 1-6 alkyl, aryl or arylC 1-6 alkyl, and wherein R 4 is C 1-6 alkyl.

17. A method according to claim 1 wherein R 1 , R 3 and R 4 each independently are methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl or pentyl.

18. A method according to claim 1 wherein P 1 and P 2 together form an acid labile vicinal-diol protecting group.

19. A method according to claim 1 wherein P 1 and P 2 is a dialkyl methylene radical.

20. A method according to claim 4 wherein R 5 is hydrogen, R 1 O—C(═O)—, (R 6 ) 3 P=wherein R 6 is alkyl, aryl or aralkyl, or (R 7 O) 2 P(═O)— wherein R 7 is alkyl, aryl, aralkyl.

21. An intermediate having the formula (3),

wherein P 1 and P 2 represent each independently a hydrogen, a hydroxy-protecting group or may together form a vicinal-diol protecting group, R 1 represents alkyl, aryl or aralkyl, R 2 represents hydrogen or C(═O)OR 3 , R 3 represents alkyl, aryl or aralkyl, or R 3 , if present, and R 1 taken together with the atoms to which they are attached may form a 6 to 8-membered cyclic group which may be optionally substituted with alkyl, aralkyl, or aryl;

provided that when R 2 is hydrogen and P 1 and P 2 taken together form an isopropylidene, then R 1 is other than methyl or ethyl.

22. An intermediate having the formula (4) or (4′),

wherein R 1 represents alkyl, aryl or aralkyl; R 2 represents hydrogen or C(═O)OR 3 ; R 3 represents alkyl, aryl or aralkyl, or R 3 , if present, and R 1 taken together with the atoms to which they are attached may form a 6 to 8-membered cyclic group which may be optionally substituted with alkyl, aralkyl, or aryl; OR 4 represents an alcoholate.

23. An intermediate having the formula (5) or (5′),

wherein OR 4 represents an alcoholate.

24. An intermediate according to claim 23 wherein the intermediate has the formula (5a)

25. An intermediate according to claim 24 in crystalline form.