Cooperative Photoredox/Gold Catalysed Cyclization of 2-Alkynylbenzoates with Arenediazonium Salts: Synthesis of 3,4- disubstituted Isocoumarins

Several isocoumarins have been synthesized in good to excellent yields starting from 2-alkynylbenzoates and arenediazonium salts. The strategy involves a domino arylation/oxo-cyclization catalysed by a dual photoredox/gold catalytic system. The reactions run under mild conditions at room temperature in wet acetonitrile under irradiation with a blue-led lamp, in the presence of a cationic gold catalyst and a cheap organic photocatalyst. The scope is quite broad and allows the preparation of isocoumarins differently disubstituted in positions 3 and 4. A plausible reaction mechanism is proposed.