New chromones from Spathelia sorbifolia L. (Rutaceae); synthesis of the benzo[1,2-b:3,4-b′]dipyranone sorbifolin

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Abstract
Ten more chromones containing both 2,2-dimethylchromen and 2-methylchromone entities, all derivatives of 5,7-dihydroxy-2-methylchromone, have been isolated from Spathelia sorbifoliaL. and characterised. These are allopteroxylin (6), spatheliachromen (9), spatheliabischromen (4), methylallopteroxylin (8), methylsorbifolin (2), methylisospatheliachromen (19), anhydrosorbifolin (33). 6-(3-methylbut-2-enyl)allopteroxylin (28), 10-(3-methylbut-2-enyl)spatheliachromen (21), and 10-(3-methylbut-2-enoyl)spatheliachromen (23). Sorbifolin (1) has been synthesised via the reaction of singlet oxygen with the acetate of (28).