Extreme Oxatriquinanes: Structural Characterization of α‑Oxyoxonium Species with Extraordinarily Long Carbon–Oxygen Bonds

The first stable α-oxyoxonium species have been synthesized and characterized. Strong donation of nonbonding electrons on oxygen into the adjacent σ*­(C–O+) orbital was predicted by modeling to result in unheard of carbon–oxygen bond lengths. The kinetic stability of the triquinane ring system provides a platform upon which to study these otherwise elusive species, which are evocative of intermediates on the acetalization reaction pathway. Crystallographic analysis of the α-hydroxy and α-methoxy oxatriquinane triflates reveals 1.658 and 1.619 Å C–O+ bond lengths, respectively, the former of which is a new record for the C–O bond.