反应详情

A stirred solution of 5-allylcyclopent-2-enone (2.20 g, 18 mmol), t-butyl carbamate (4.70 g, 40 mmol), and tetra-n-butylammonium bromide (6.45 g, 20 mmol) in anhydrous dichloromethane (40 mL) under nitrogen was cooled in an ice bath (3° C.) and treated dropwise with boron trifluoride etherate (2.22 mL, 18 mmol). The reaction mixture was allowed to warm to room temperature and stirred for 18 h. Saturated aqueous sodium bicarbonate (40 mL) was added and then mixture stirred for 15 min and separated. The aqueous solution was extracted with dichloromethane (2×20 mL) and the combined organic solution was washed with water and saturated aqueous sodium chloride (20 mL each), dried (Na2SO4), and concentrated in vacuo. The residue was dissolved in minimum dichloromethane and added to a column of silica gel (˜300 cc) and eluted first with 85:15 heptane/ethyl acetate to afford recovered starting material (0.35 g), then with 4:1 heptane/ethyl acetate to afford a mixture of t-butyl carbamate and subject compound. This mixture was warmed in heptane and filtered to remove most of the t-butyl carbamate, then the filtrate was added to a column of silica gel (˜300 cc) and eluted with 6:3:1 heptane/dichloromethane/ethyl acetate to afford tert-butyl 3-allyl-4-oxocyclopentylcarbamate 1.17 g (27%) as a pale amber solid. NMR (CDCl3): δ 5.60-5.75 (m, 1 H), 4.90-5.05 (m, 2 H), 4.50 (br s, 1 H), 4.00-4.25 (m, 1 H), 2.30-2.80 (m, 3 H), 2.20-2.30 (m, 1 H), 1.85-2.15 (m, 3 H), 1.38 (s, 9 H). MS (M+1): 240.1.

1. stirringmixture stirred for 15 min
2. customseparated
3. extractionThe aqueous solution was extracted with dichloromethane (2×20 mL)
4. washthe combined organic solution was washed with water and saturated aqueous sodium chloride (20 mL each)
5. dry with materialdried (Na2SO4)
6. concentrationconcentrated in vacuo
7. dissolutionThe residue was dissolved in minimum dichloromethane
8. additionadded to a column of silica gel (˜300 cc)
9. washeluted first with 85:15 heptane/ethyl acetate
10. customto afford
11. customrecovered
12. customwith 4:1 heptane/ethyl acetate to afford
13. filtrationfiltered
14. customto remove most of the t-butyl carbamate
15. additionthe filtrate was added to a column of silica gel (˜300 cc)
16. washeluted with 6:3:1 heptane/dichloromethane/ethyl acetate