AbstractTreatment of 3,4‐benzoxanthone hydrazone with tetrahalogeno‐α‐benzoquinones gave the corresponding cyclic ethers (IIIa‐b). Reductive cleavage of the latter with lithium aluminium hydride yielded 3,4‐benzoxanthene together with the tetrahalogenocatechol. Whereas active hydrogen compounds effect cleavage of the dioxole ring in IIIa‐b with the formation of the corresponding benzo‐xanthylene, they react with 9‐hydroxy‐3,4‐benzoxanthene yielding the benzoxanthyl derivatives (VIII).Diazoalkanes on 3,4‐benzoxanthione afford the corresponding ethylene sulfides. The thermochromic properties of the ethylenes, obtained by the action of copper on the ethylene sulfides, are stressed.Reaction mechanisms are discussed.