Ring Synthesis of Isocoumarins

One approach to isocoumarins is comparable to that above for 2-benzopyryliums, but replacing the aromatic aldehyde with an acid group.  

Benzoates carrying an orf/to-acetylenic substituent, from Sonogashira couplings (4.2.5.1), can be ring closed using mercuric acetate, which also allows the introduction of an iodine at C-4, ° or if that functionality is not required, simple acid-catalysed closure works well. The use of iodine chloride similarly gives 

The most general route involves coupling an alkyne with ort/to-iodobenzoic acid or with methyl ortho-iodobenzoate. Both mono- (giving 3-substituted isocoumarins ) and disubstituted alkynes will serve, allowing considerable flexibility for the construction of substituted isocoumarins. 

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