Regiospecific synthesis of alkylphenanthrenes using a combined directed ortho metalation (DoM) - Suzuki-Miyaura cross coupling - directed remote metalation (DreM) methodology

A literature survey on the syntheses of phenanthrenes is reviewed. These syntheses have limitations, e.g. lack of regioselectivity and difficulty in preparation in multi-gram scale. Suzuki-Miyaura cross coupling reactions are discussed on various topics, i.e. bases, solvents, steric hindrance and tolerance of functional groups respectively. A combined directed ortho metalation (DoM) - Suzuki-Miyaura cross coupling route is used for regiospecific synthesis of alkylphenanthrenes. The highly pure alkylphenanthrenes, 1-methyl- (128), 1,7-dimethyl- (135), 7-ethyl-1-methyl- (145) and 7-t-butyl-1-methylphenanthrene (149) have been synthesized in overall yield 21--36% and 4--7 steps. Carbonylative amination of triflates has been investigated, showing that inexpensive phenols can serve as a starting material for the preparation of N, N-diethylbenzamides, which, in turn, are potential point for the DoM chemistry.