反应详情

Boron trifluoride etherate (5 μl) was added to a suspension of (3R,4R)-4-(2-hydroxyethyl)-3-phthalimidoazetidin-2-one (126 mg) and 2,2-dimethoxypropane (74 μl) in dichloromethane (3 ml) at ambient temperature. The mixture was stirred for two hours. Additional dimethoxypropane (50 μl) was added and the mixture was stirred for an additional 1.5 hours. The resulting solution was poured into a saturated aqueous solution of sodium chloride and sodium bicarbonate and extracted twice with dichloromethane. The combined extracts were dried over magnesium sulfate and evaporated to give a crystalline solid. Chromatography on silica gel (4 g; eluting with 3% acetone in dichloromethane) and washing the crystals with ether afforded 100 mg of (6R,7R)-2,2-dimethyl-7-phthalimido-1-aza-3-oxabicyclo[4.2.0]-octan-8-one: IR (CH2Cl2): 1770 and 1720 cm-1 ; NMR (CDCl3) δ: 1.56 (s, 3H), 1.81 (s, 3H), 1.7-2.0 (m, 2H), 3.7-4.1 (m, 3H), 5.01 (d, J=2 Hz, 1H), and 7.5-7.9 (m, 4H).

1. stirringthe mixture was stirred for an additional 1.5 hours
2. extractionextracted twice with dichloromethane
3. dry with materialThe combined extracts were dried over magnesium sulfate
4. customevaporated
5. customto give a crystalline solid
6. washChromatography on silica gel (4 g; eluting with 3% acetone in dichloromethane) and washing the crystals with ether