What is "barrelene"

n. (context organic compound English) The bicyclic organic compound ''bicyclo[2.2.2]octa-2,5,7-triene''

Barrelene is a bicyclic organic compound with chemical formula CH and systematic name bicyclo[2.2.2]octa-2,5,7-triene. First synthesized and described by H. E. Zimmerman in 1960 the name derives from the obvious resemblance to a barrel, with the staves being three ethylene units attached to two methine groups. It is the formal Diels-Alder adduct of benzene and acetylene. Due to its unusual molecular geometry the compound is of considerable interest to theoretical chemists. Like benzene, barrelene has a set of 6 cyclic, but not planar, overlapping p-orbitals. Because of overlap of opposite-sign lobes, the structure represents Möbius aromaticity.

Triptycenes, with the alkene groups part of an arene, are related compounds. It is also a starting material for many other organic compounds such as semibullvalene.

The original Zimmerman synthesis modified in 1969 starts from coumalic acid:

(* The conversion of the bis-N-tosyl-imine into the bis-N-tosylacetamide analog, by mean of NaHCO3/Dioxane, seems a misprint. In fact the oxidation level of the tosylamide is one notch higher than tosylimine, but no oxidizing agent is reported. Maybe hydrogen peroxyde in place of water could have been cited in original work ?)

many alternative routes have been devised since then, one of them starting from oxepin:

An alternate route that allows synthesis of the parent barrelene system and a variety of substituted barrelenes has also been reported