Ammonia → 4,5-Dihydro-1H-isoindole-1,3(2H)-dione

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The 3-substituted phthalimidines of formula (I) wherein Z is OH can be prepared by reacting, under nondehydrating conditions, equivalent amounts of a 3-substituted phthalide of the formula ##STR3## wherein R, X, Y, a and b have the same meanings as above, and ammonia, or a primary aliphatic or aromatic amine. The reaction is preferably carried out in the presence of an inert organic solvent for the phthalide such as tetrahydrofuran, diethyl ether, diisopropyl ether, methyl n-butyl ether and the like. The solvent should have a boiling point below about 100° C. to permit ready separation from the reaction product by distillation at moderate temperatures. This serves to minimize dehydration of the 3-hydroxy group on the phthalimidine product. The primary amines employed in the reaction are those of the formula H2N--Q where Q has the same meaning as above. When the reaction is conducted at temperatures above about 100° C., dehydration takes place to produce a 3-substituted phthalimidine of formula (II).

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