Isoindoles, benzo[c]thiophenes and isobenzofurans: reactions and synthesis

The phthalocyanine macrocyclic system, formally derived from isoindoles, is the basis for many blue dyestuffs. Metal derivatives have a cation complexed at the centre, much as the iron atom in haem. Partial oxidation of 1,2-bishydroxymethylbenzene produces 1-methoxy-1,3-dihydroisobenzofuran, from which methanol can be eliminated, using LDA, giving isobenzofuran. The position of such tautomeric equilibria can be altered by changing solvent – solvents such as DMSO tend to favour the N-hydrogen tautomer, where protic solvents like alcohols favour the imine tautomer. N-Substituted isoindoles, too, have generally been made from an isoindoline by elimination processes, thus N-oxides can be made to lose water by pyrolysis or better, by treatment with acetic anhydride. Phthalocyanine can be produced by the reductive cyclisation of 2-cyanobenzamide or, in a route which makes its relationship to isoindole more obvious, by the combination of four molecules of 1,3-diiminoisoindoline with the elimination of ammonia.