We have developed a metal-free and highly diastereoselective ammonium-directed dihydroxylation of 3-aminocyclohex-1-enes upon treatment with Cl₃CCO₂H followed by mCPBA. The reaction mechanism involves protection of the amine by protonation, hydrogen-bonded delivery of the oxidant by the allylic ammonium ion formed in situ, followed by highly regioselective ring-opening of the intermediate syn-epoxide by trichloroacetic acid, to give a 1,2-anti-2,3-syn amino diol after deprotection. Meanwhile, oxidation of the corresponding tertiary amine N-oxide is entirely complementary and proceeds with high anti-diastereoselectivity to afford the corresponding 1,2-anti-2,3-anti amino diol after deprotection, consistent with the epoxidation reaction proceeding under steric or dipole control. The ammonium-directed oxidation protocol is general for a range of cyclic allylic and homoallylic amines and facilitates the metal-free synthesis of all four diastereoisomers of the corresponding 3-amino-1,2-diols, and has recently been employed as one of the key steps in the syntheses of (±)-1-deoxynojirimycin and (±)-1-deoxyaltronojirimycin.