3,3,6,10b-Tetramethyl-4a,10b-dihydronaphtho[2,1-e][ 1,2,4]trioxane and its 3,3-spirocyclic cyclopentane analogue on treatment with an excess of trimethylsilyl trifluoromethanesulphonate for 10 min at 24 °C rearrange to give 2-(2-oxopropyl)-3-methyl-1-benzofuran in high yield; in similar fashion the 3-methyl, n-butyl, and phenyl derivatives of 3,10b-epidioxy-2,3,4a,10b-tetrahydro-6-methyl-1H-naphtho[2,1-b] pyran give the 3-oxobutyl, 3-oxoheptyl, and 3-phenyl-3-oxopropyl derivatives of 2-formyl-3-methyl(2H)-1-benzopyran.