2,3-Dihydroxy-4-methoxybenzoic acid → 7-methoxy-2',3',5',6'-tetrahydro-Spiro[1,3-benzodioxole-2,4'-(4H)-pyran]-4-carboxylic acid

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Reaction Steps

A suspension of 2,3-dihydroxy-4-methoxybenzoic acid (6.04 g, 32.8 mmol) in 5,6-dihydro-4-methoxy-2H-pyran (20 mL, 152 mmol) was kept at 140° C. for three days. At room temperature ethyl acetate (200 mL) was added and the organic phase was extracted with saturated aqueous NaHCO3 (2×50 mL). The aqueous phase was washed with Et2O (2×40 mL), acidified to pH=1 with concentrated HCl and extracted with dichloromethane (2×50 mL). The organic phase was dried over MgSO4. Evaporation under reduced pressure afforded traces of 2,3-dihydroxy-4-methoxybenzoic acid along with 7-methoxy-2′,3′,5′,6′-tetrahydro-Spiro[1,3-benzodioxole-2,4′-(4H)-pyran]-4-carboxylic acid (1.23 g, 14%). 13C NMR (DMSO) δ 164.9, 148.2, 146.6, 134.5, 123.7, 117.0, 107.1, 106.8, 64.4, 56.0, 35.3.

Provenance & Evidence