Acid Red 94

Typical Procedure (R¹=CH₃, R²=R³=H): 2-Methylfuran (82.1mg, 1.0 mmol) is dissolved in methanol (6 mL) containing rose Bengal (102 mg, 0.1 mmol). The solution is cooled with an ice bath. Oxygen gas is gently bubbled through the solutions while it is irradiated with a xenon Variac Eimac Cermax 300 W lamp. After completion of the reaction (usually 8 min), methyl sulfide (249 mg, 4.0 mmol) is added for the reduction of the hydroperoxy group. After completion of the reduction (1 h), homoveratrylamine [D0678] is added (145 mg, 0.8 mmol) and the mixture is stirred for 30 min at room temperature. After the formation of the intermediate 2-pyrrolidinone, methanol is replaced by CH₂Cl₂ (4 mL). TFA (91.2 mg, 0.8 mmol) is added in CH₂Cl₂ (2 mL) and the mixture was stirred for 6 more hours at room temperature. After concentration of the solution, the product is purified by silica gel flash column chromatography (eluent: petroleum ether:EtOAc = 1:1) to give the desired aromatic tricyclic product (125 mg, 60%).