Thiophen Analogues of Phenanthrene

Thiophen Analogues of Phenanthrene.— Electrophilic substitutions of naphtho[2,l-6]thiophen (434) such as nitration, formylation, and acylation occur, in contrast to those in benzo[6]thiophen, in the thiophenic a-position (2-position). Bromination gives a mixture of the 2-bromo- and 2,5-dibromo-derivatives. That the 5-position is the second most reactive 

One of the missing dithiophen analogues (439) was prepared from 4,4 -diformyl-3,3 -bithienyl by slowly distilling a mixture of this dialdehyde, 

---