SYNTHESIS OF 3-ARYLISOCOUMARINS, INCLUDING THUNBERGINOLS A AND B, UNSYMMETRICAL 3,4-DISUBSTITUTED ISOCOUMARINS, AND 3-YLIDENEPHTHALIDES VIA IODOLACTONIZATION OF METHYL 2-YNYLBENZOATES OR THE CORRESPONDING CARBOXYLIC ACIDS”

3-Aryl-4-iodoisocoumarins, which were readily and efficiently prepared by regioselective iodolactonization of methyl 2-ynylbenzoatesor the corresponding carboxylic acids, were used as precursors either to 3-arylisocoumarins, including naturally-occurring thunberginols or to unsymmetrical 3,4-disubstituted isocoumarins. On the other hand, (Z)- and (E)-3-iodomethylidenephthalides, which were regioselectively prepared by iodolactonization of methyl 2-ethynylbenzoate, were employed as starting materials for the stereospecific synthesis of (Z)- and (E)-3-ylidenephthalides, respectively. Some 3-arylisocoumarins and unsymmetrical 3,4-disubstituted isocoumarins showed certain cytotoxic activity against human cancer cell lines in vitro