反应详情

温度

145 °C

P-Toluenesulfonic acid (97 mg, 0.51 mmol) was added to 4,4-dimethoxytetrahydro-(4H)-thiopyran (20.7 g, 128 mmol) and the mixture was heated to 145° C. and kept at that temperature until approximately one equivalent of methanol (5.17 mL, 128 mmol) was distilled off. The mixture was then cooled to 130° C. and distillation under reduced pressure afforded 10.1 g of a 5:3 mixture of 5,6-dihydro-4-methoxy-(2H)-thiopyran [1H NMR (DMSO) δ 4.87 (m, 1H), 3.44 (s, 3H), 3.15 (dt, 2H), 2.72 (t, 2H), 2.22 (m, 2H)] and 4,4-dimethoxytetrahydro-(4H)-thiopyran. Without further purification the mixture was added to 2,3-dihydroxy-4-methoxybenzoic acid (2.00 g, 10.9 mmol) and the suspension was exposed to microwave heating (180° C., one hour) in a sealed reaction vessel. Ethyl acetate (100 mL) was added and the organic phase was first washed with 0.5 M HCl (40 mL) and then extracted with saturated aqueous NaHCO3 (2×30 mL). The aqueous phase was washed with Et2O (2×40 mL), acidified to pH=1 with concentrated HCl and extracted with dichloromethane (2×30 mL). The organic phase was dried over MgSO4. Evaporation under reduced pressure afforded 7-methoxy-2′,3′,5′,6′-tetrahydro-spiro[1,3-benzodioxole-2,4′-(4H)-thiopyran]-4-carboxylic acid (1.86 g, 61%). 13C NMR (DMSO) δ 164.9, 148.2, 146.6, 134.5, 123.8, 118.0, 107.2, 106.9, 56.1, 35.9, 25.4.

1. distillationwas distilled off
2. temperatureThe mixture was then cooled to 130° C.
3. distillationdistillation under reduced pressure
4. customafforded
5. customWithout further purification the mixture
6. temperatureheating (180° C., one hour)
7. customin a sealed reaction vessel
8. washthe organic phase was first washed with 0.5 M HCl (40 mL)
9. extractionextracted with saturated aqueous NaHCO3 (2×30 mL)
10. washThe aqueous phase was washed with Et2O (2×40 mL)
11. extractionextracted with dichloromethane (2×30 mL)
12. dry with materialThe organic phase was dried over MgSO4
13. customEvaporation under reduced pressure