A Convergent Approach to the Dioxaadamantane Core of (±)-Tetrodotoxin

A fully stereocontrolled 1,3-diol orthoesterification and a water-promoted intramolecular Henry addition, combined with the previously reported formal (3 + 3) annulation of α-nitro-α,β-enals and 2,2-dimethyl-1,3-dioxan-5-one, provided for a short convergent pathway to the dioxaadamantane core of (±)-tetrodotoxin.