Regiospecific Synthesis of Dimethylphenanthrenes

The dimethylated phenanthrenes 2,3-dimethylphenanthrene (4a), 2,7-dimethylphenanthrene (4b), 2,6-dimethylphenanthrene (4c) and 1,7-dimethylphenanthrene (4d) have been prepared in gram-quantities by a short sequence of directed ortho metalation (DoM) of N,N-diethylbenzamides followed by Suzuki–Miyaura cross-coupling reaction and directed remote metalation (DreM) to form 9-phenanthrols. The final phenanthrenes were obtained through protection/deprotection as triflates.