Question

What is the IUPAC name of the compound below?

Answer 1

Hint: Fused heterocycles are the systems which are constructed by combining two or more rings. The rings are fused in such a way that each ring in the compound shares one common fusion bond. The fused heterocycles can be of two types i.e., aromatic carbocyclic linked to heterocycle and heterocycle linked to another heterocycle.

Complete answer:
For IUPAC nomenclature of fused heterocyclic compounds, first we have to identify the root name of the compound and then the name of the substituent groups or functional groups will be named accordingly.
Now, for the given compound, first if we just see the ring and not the functional group i.e., ketonic group, it is clearly visible that the heterocyclic ring is fused with aromatic carbocycle i.e., benzene ring and the fusion of bond can diagrammatically be represented as follows:

Here, the base (trivial) name of the heterocycle is indoline and as the fusion takes place at the c position so, iso prefix is introduced with the base name i.e., indoline. Now, if we add the ketonic group to indoline as given in the question, the numbering always starts from the functional group present at prior in the heterocyclic ring. So, the IUPAC name of the compound will be as follows:

Thus, we can conclude that the IUPAC name of the given compound is Isoindoline-1,3-dione.

Note:
The common name of the given compound is Phthalimide. It is important to note that the method which we used to name the given compound is the common nomenclature for fused heterocycles in which the names are derived from trivial names of compounds. There are two more methods which can be used for nomenclature of fused heterocycles which are the replacement method and the Hantzsch-Widman method.