Alkylated dodecahydronaphtho[2,1-b]furans of the general formula I ##STR1## where R.sup.1 and R.sup.2 are identical and each is hydrogen or methyl are prepared by reacting alkylated 2-hydroxydecahydronaphthalene-1-ethanol of the formula II ##STR2## where R.sup.1 and R.sup.2 are as defined above, with a sulfonyl chloride in the presence of basic catalysts by performing the cyclization in the presence of concentrated aqueous alkali metal hydroxides and a phase transfer catalyst, preferably a tetra-substituted ammonium or phosphonium salt, the sulfonyl chloride used preferably comprising a sulfonyl chloride of the general formula IIIR.sub.3 -SO.sub.2 Clwhere R.sup.3 is C.sub.1 -C.sub.3 -alkyl or phenyl which may be substituted in the para position by methyl, chlorine, bromine or nitro.