Synthesis via pummerer intermediates. IV . Synthesis of 1‐(4‐hydroxy‐2‐oxo‐2 H ‐1‐benzopyran‐3‐yl)pyridinium hydroxide inner salt derivatives and 3‐(2 H )benzofuranones by the action of phosgene in pyridine on 2‐hydroxy‐1‐[(methylsulfinyl)acetyl]benzene derivatives

The treatment of ketosulfoxide 1 with phosgene in pyridine gave a mixture of 1‐(4‐hydroxy‐8‐methoxy‐2‐oxo‐2 H ‐1‐benzopyran‐3‐yl)pyridinium hydroxide inner salt ( 4 ) and 7‐methoxy‐2‐(methylthio)‐3‐(2 H )benzofuranone ( 7 ). Ketosulfoxides 8 and 11 behaved similarly. The inner salt structure assigned to compounds 4, 10 , and 13 was confirmed by the unambiguous synthesis of 10 and 13 from hydroxycoumarins 15 and 18 .