Abstract7‐Chloro‐2‐chloromethyl‐benzofuran(13)and 3, 8‐dichloro‐2 H‐1‐benzopyran(12)are the main products from the thermal rearrangement (230–260°) of 2, 6‐dichlorophenyl propargyl ether(7). Compounds17,18and19are also formed, but in much smaller amounts (scheme 2 and table 1). However, in the case of the bromo‐compounds8and9the rearrangement products are the benzofuran derivatives21and22, containing one bromine atom less per molecule (scheme 4).The corresponding naphthyl propargyl ethers10and11can be rearranged much more easily (180°) to the halogeno‐naphthofurans24and26respectively. In the case of the bromo‐ether11, 2‐methyl‐naphtho[2, 1‐b]furan(25)is also formed (scheme 5).If the propargylic hydrogen atoms in7and11are replaced by deuterium atoms, then after rearrangement the deuterium atoms in the products d‐13and d‐26are found in the β‐positions to the oxygen atom of the furan ring (schemes 3 and 5).It is suggested that initially a [3s, 3s]‐sigmatropic rearrangement of the aryl propargyl ethers to the 6‐allenyl‐6‐halogeno‐cyclohexa‐2, 4‐dien‐1‐ones (e.g.a) occurs and that from these the isolated products are formedviaradical pathways (scheme 6).Under neutral conditions aryl propargyl ethers containing a freeortho‐position give on heating benzopyran derivatives [2]. When this thermal reaction is carried out in sulfolane in the presence of powdered potassium carbonate,2‐methyl‐benzofuran derivatives are formed (table2). This leads to the possibility of preparing, depending on the conditions, either benzopyran or benzofuran derivatives by theClaisenrearrangement of aryl propargyl ethers. The mec