The action of aqueous hydrochloric, hydrobromic and trifluoroacetic and formic acids with amberlyst-15 as catalyst on the 1,4-endoperoxide of 1,4-dimethylnaphthalene afforded the monochloro and analogously substituted 1-methyl derivatives of the last compound. Acid catalysis of the endoperoxide in the presence of aldehydes and ketones gave the cis fused 3-derivatives of 6,10b-dimethyl-4a,10b-dihydronaphtho[2,1-e]-1,2,4-trioxin in high yields. The trioxanes obtained from formaldehyde were converted quantitatively on treatment with benzylamine in dichloromethane into their corresponding cis 1,2-diols. An equivalent of trimethylsilyl trifluoromethanesulfonate on 3,3,6, 1Ob-tetrarnethyl-4a,10b-dihydronaphtho[2, 1-e]-1,2,4-trioxin furnished 2-(2-oxopropyl)-3-methylbenzo[b]furan exclusively.