An Unexpected Synthesis of Crowded Triphenylenes

In attempts to make octaphenyldibenzofuran (7) and octaphenyldibenzothiophene (8), 2,5‐dibromofuran (4) 2,5‐dibromothiophene (5), respectively, were heated with tetracyclone (2) under forcing conditions, but only single addition products, such as 2‐bromo‐4,5,6,7‐tetraphenylbenzofuran (10) 2‐bromo‐4,5,6,7‐tetraphenylbenzothiophene (12) observed. However, when 2,5‐dibromothiophene‐1,1‐dioxide (6) was tetracyclone, the chief product 1,2,3,4,6,7,8‐heptaphenyltriphenylene (14). Similarly, compound 6 acecyclone (15), 11,18,20‐triphenyldiacenaphtho[a,h]triphenylene (16). Both 14 16 have been characterized by X‐ray crystallography. They are proposed form from double Diels‐Alder products of cyclopentadienones extrusion sulfur dioxide rearrangement resulting radicals.