The cyclic molecule furan (C₄H₄O) has been the subject of several unsuccessful astronomical searches going back to 1972, when Dezafra and coworkers sought for its 1₁₀-1₁₁ rotational transition at 4575.9 MHz in 9 sources including NGC 2024 (the Flame nebula), Cas A (a supernova remnant), and commonly scanned objects such as IRC+10216, the Orion A nebula, and Sgr B2, using the 140 ft Green Bank telescope. In 1980, Kutner and coworkers searched for two additional rotational transitions, at 10.584 and 88.748 GHz, in Orion A and Sgr B2 without success. Finally, in 2001 Dickens and coworkers reported that they were not able to detect any of 6 rotational transitions in various sources in a multitelescope effort.

Furan is one of the simplest five-membered organic ring compounds with a heteroatom substituted for a carbon atom. This gives furan a dipole moment and enables a pure rotational spectra. Furan is an intriguing molecule to search for in space because it is a precursor to ribose and deoxyribose, which are critical components of both DNA and RNA. Furan is aromatic, as indicated by the manner in which the pi orbitals overlap around the ring as depicted in the image to the right.