To obtain the subject compound in high yield by directly nitrating dialkyl phthalates and reducing the resultant nitrophthalic acid dialkyl ester.

Dialkyl phthalates (dimethyl phthalate) of formula I (R1 and R2 are each an alkyl or a cycloalkyl) is nitrated with oxygen or air containing nitrogen oxide and ozone, preferably by using a catalyst, preferably comprising a metal and/or a compound of the metal (e.g. iron or ferrous chloride) at -30 to 100°C to afford a dialkyl nitrophthalate of formula II (e.g. dimethyl 5- nitroisophthalate) and reducing the resultant compound at 0-300°C to provide the objective compound of formula III (e.g. diisopropyl 5-aminoisophthalate).