反应详情

A mixture of the cyclopentenol obtained according to Example 1 (5 g, 32.5 mmol) with triethyl orthoacetate (47.2 ml=42.1 g, 260 mmole, 8 eq.) was heated to 145° (temp. of oil bath 160°) under a nitrogen current in a reactor which was equipped with a Vigreux column and a condenser, while adding continuously, over 4 h, pivalic acid (232 mg, 2.28 mmole, 7 mol %) in triethyl orthoacetate (5.9 ml=5.26 g, 32.5 mmole, 1 eq.). During the reaction, the formed ethanol, as well as the ethyl acetate and a little orthoacetate, were removed by distillation. The reaction mixture was heated for 1 more hour, then cooled to 20°, hydrolyzed with diluted aqueous NaHCO3 and extracted with ether. The organic layer was washed 2× with water and once with brine, dried over Na2SO4 and evaporated, to give 15.4 g of crude product. After distillation of the heads (6.6 g, 50°/1.1×102Pa), 5.30 g (95°/1.1×102Pa) of (+)-ethyl (1R)-2-pentyl-2-cyclopentene-1-acetate were obtained (yield 73%), having an enantiomeric purity of 90% e.e. (chiral column of the type Megadex®5).

1. customobtained
2. temperaturewas heated to 145° (temp. of oil bath 160°) under a nitrogen current in a reactor which
3. customwas equipped with a Vigreux column and a condenser
4. additionwhile adding continuously, over 4 h
5. customDuring the reaction
6. customthe formed ethanol, as well as the ethyl acetate and a little orthoacetate, were removed by distillation
7. temperatureThe reaction mixture was heated for 1 more hour
8. temperaturecooled to 20°, hydrolyzed with diluted aqueous NaHCO3
9. extractionextracted with ether
10. washThe organic layer was washed 2× with water
11. dry with materialonce with brine, dried over Na2SO4
12. customevaporated
13. customto give 15.4 g of crude product
14. distillationAfter distillation of the heads (6.6 g, 50°/1.1×102Pa)