反应详情

A solution of 3.68 g (21.9 mmol) of 4a in 60 mL of benzene with 416 mg (2.19 mmol) of p-toluenesulfonic acid monohydrate was heated in an oil bath at 100-110° C. for 24 h. A mini Dean-Stark trap was used for azeotropic distillation. Benzene was evaporated on a rotary evaporator, and the residue was treated with 2N aqueous Na2CO3 solution. The basic aqueous solution was washed with ether, then acidified to pH 2 with hydrochloric acid, and again extracted with ether. The combined ether extracts were washed with water, brine, dried, and concentrated to give 2.87 g (17.1 mmol, 78% yield) of 5a as clear oil after chromatography (silica gel, eluted with 20% to 25% of ethyl acetate in hexanes). Optical purity: 79% ee (after methylation); [α]24D−22.0 (c 0.1, MeOH); 1H NMR (CDCl3): δ 1.19 (3H, s), 1.37 (3H, s), 1.48 (3H, s), 1.58 (3H, s), 2.55 (1H, m), 2.81 (2H, m); 13C NMR (C6D6): δ 183.49, 135.57, 123.27, 47.47, 45.09, 28.15, 25.94, 22.09, 19.51, 18.52; EI-MS m/z (%): 168 [M]+ (38), 153 (38), 135 (8), 125 (21), 123 (27), 107 (59), 93 (29), 81 (100), 67 (30), 53 (16), 41 (25); HREIMS: obsd. 168.1152, calcd. for C10H16O2 (M+): 168.1150.

1. distillationA mini Dean-Stark trap was used for azeotropic distillation
2. customBenzene was evaporated on a rotary evaporator
3. additionthe residue was treated with 2N aqueous Na2CO3 solution
4. washThe basic aqueous solution was washed with ether
5. extractionagain extracted with ether
6. washThe combined ether extracts were washed with water, brine
7. customdried
8. concentrationconcentrated