1,4-Dioxin 1,2-Dioxin is a heterocyclic, organic, antiaromatic[1] compound with the chemical formula C4H4O2.

Due to its peroxide-like characteristics, 1,2-dioxin is very unstable and has not been isolated.

Calculations suggest that it would isomerize rapidly into but-2-enedial.

[3] In 1990, 3,6-bis(p-tolyl)-1,2-dioxin (1) was incorrectly reported as the first stable derivative.

[4] It was subsequently shown that the initial compound was not a derivative of 1,2-dioxin, but a thermodynamically more stable dione (2).