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.