An Unexpected Synthesis of Crowded Triphenylenes

Abstract

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