Oxatriquinane


Oxatriquinane is an alkyl oxonium ion with formula, remarkable for being stable in aqueous solution. It has a cyclononane backbone, with a trivalent oxygen connected to carbon 1, 4, and 7, forming three fused pentagonal rings.

History

Oxatriquinane was first described in 2008, and was obtained after a five-step synthesis starting from 1,4,7-cyclononatriene.
At the time it had the longest C–O bond lengths and most acute C−O−C angles ever observed in a compound.

Reactions

Oxonium ions normally are strong alkylating agents and are only observed in solution as reactive intermediates or under extreme conditions. Oxatriquinane is an exception: it does not react with boiling water or with alcohols, thiols, halide ions, or amines, although it does react with stronger nucleophiles such as hydroxide, cyanide, and azide.
The ability of the oxygen to enter into a fourth covalent bond has been of some theoretical interest and was achieved using carborane acid.

Analogues

Related species include oxatriquinacene, the tri-unsaturated analogue, which is of interest as a possible precursor to oxaacepentalene, a neutral aromatic species. 1,4,7-tri-tert-butyloxatriquinane has also been synthesised; this compound contains significant amounts of intramolecular steric strain, resulting in further bond elongation to give C–O bond lengths of 1.622 Å, the longest recorded in any species.