Method of preparing (6R)-3-hexyl-4-hydroxy-6-undecyl-5, 6-dihydropyran-2-one, and intermediate used in the method

1. A method of preparing a (6R)-3-hexyl-4-hydroxy-6-undecyl-5,6-dihydropyran-2-one of formula (I), which comprises:

1) subjecting a compound of formula (II) to a reaction with a compound of formula (III) in the presence of zinc;

2) treating a resulting reaction mixture with an aqueous acid to produce a precipitate;

3) washing the precipitate with an organic solvent to obtain an organic layer; and

4) subjecting the organic layer to a cyclization under an acidic condition to obtain (6R)-3-hexyl-4-hydroxy-6-undecyl-5,6-dihydropyran-2-one of formula (I):

wherein,

P′ is hydrogen or a protecting group selected from trialkylsilyl and alkoxyalkyl which can be deprotected under an acidic condition, and

R is methyl, ethyl, or propyl.

2. The method of claim 1 , wherein P′ is hydrogen, and R is methyl, ethyl, or isopropyl.

3. The method of claim 1 , wherein the alkoxyalkyl moiety is tetrahydropyranyl, 4-methoxytetrahydropyranyl, 2-methoxy-2-propyl, or 1-ethoxy-1-ethyl.

4. The method of claim 1 , wherein the compound of formula (III) is methyl 2-bromooctanoate, ethyl 2-bromooctanoate or propyl 2-bromooctanoate.

5. The method of claim 1 , wherein zinc is used in an amount ranging from 1 to 10 molar equivalents, based on 1 mole of the compound of formula (II) used in step 1).

6. The method of claim 1 , wherein step 1) further comprises adding an additive selected from the group consisting of I 2 , 1,2-ethanedibromide, methanesulfonic acid, and trimethylsilyl chloride.

7. The method of claim 1 , wherein step 1) further comprises adding lead.

8. The method of claim 1 , wherein step 1) is carried out in a solvent selected from the group consisting of ethyl ether, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, acetonitrile, methyl acetate, ethyl acetate, benzene, toluene, and a mixture thereof.

9. The method of claim 1 , wherein the acid used in step 2) is an inorganic acid selected from the group consisting of hydrochloric acid, sulfuric acid, and hydrobromic acid; an organic acid selected from the group consisting of toluenesulfonic acid, methanesulfonic acid, and camphorsulfonic acid; or a mixture thereof.

10. The method of claim 1 , wherein step 2) is carried out in a protic solvent selected from the group consisting of water, methanol, and ethanol; an aprotic solvent selected from the group consisting of ethyl ether, tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, acetonitrile, methyl acetate, ethyl acetate, benzene, and toluene; or a mixture thereof.