A number of naturally occurring isocoumarins which have been isolated from Ceratocystis fungi have been synthesised to evaluate their role as phytotoxins and phytoalexins. The route which was used was a modification of the homophthalate approach, with an improved synthesis of the homophthalate itself. This route was adapted to allow the synthesis of some 4-substituted isocoumarins, including the cis diastereomer of perimacol, a metabolite of Periconia macrospinosa. The stereochemistry of these 3,4-disubstituted dihydroisocoumarins was investigated, and in particular the correlation between nmr chemical shifts and coupling constants and relative stereochemistry was studied. 5-Methylmellein was prepared by the indanone approach in a shorter synthesis than the previously published one. An attempt to use the indanone approach to produce 3-hydroxymethyl isocoumarins failed. It was found that such compounds can be obtained by allylic functionalisation of suitably substituted isocoumarins.