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Isomerization and subsequent lithium alanate reduction of sclareolide by the method of G. Ohloff, Helv. Chim Acta, 68 (1985), 2022-29, was used to obtain a diastereoisomeric decahydro-2-hydroxy-2,5,5,8a-tetramethyl1-naphthaleneethanol (mp. 191° C.). 142 g of this diol were dissolved in 2,110 g of toluene, and the solution was admixed with 120 g (3 mol) of sodium hydroxide in 120 ml of water and then with 48 g (0.15 mol) of tetrabutylammonium bromide. 101 g (0.5 mol) of p-toluenesulfonyl chloride were then added twice in the course of 1 hour, and the reaction mixture was subsequently stirred for 2 hours, and admixed with 500 ml of water and thereafter thoroughly stirred for a further 10-20 minutes. The bottom, aqueous phase was separated off and washed once with 200 ml of water, and thereafter the solvent was distilled off at 300 mbar. Recrystallization of the residue left 121.6 g of isomeric dodecahydro-3a,6,6,9a-tetramethylnaphtho[2,1-b]furan (formula Ib; R1, R2 =CH3), of mp. 60° C. and [a]20D =+7.5°, which corresponds to a yield of 92%.