Isobenzofuran is a bicyclic heterocycle consisting of fused cyclohexa-1,3-diene and furan rings.

It is isomeric with benzofuran.

Isobenzofuran is highly reactive and rapidly polymerizes; however, it has been identified[2] and prepared by thermolysis of suitable precursors and trapped at low temperature.

[3] Though isobenzofuran itself is not stable, it is the parent of related stable compounds with more complex structures, [4] such as the hindered analogue 1,3-diphenylisobenzofuran.