The reaction of thallium triacetate and thallium trinitrate with four monoterpenic unsaturated alcohols (isopulegol, neo-isopulegol, cis-carveol and alpha-terpineol), in AcOH:H2O, (1:1, vol/vol) as solvent, led to the corresponding beta-hydroxy-cyclic ethers with high regio- and stereoselectivity, in moderate to good yields. A mechanism of ring-contraction or ring-expansion of the oxythallated adduct is proposed, based on the substitution patterns of each double bond.