Synthesis of alkylphenanthrenes from naphthylalkylidenemalonodinitriles. A route to 1-methyl-, 2-methyl-, and 1,2-dimethylphenanthrene

The study has been carried out to evaluate the feasibility of synthesis of 1-methyl-, 2-methyl-, 1,2-dimethyl-, and 1-ethyl-2-methylphenanthrene through the annulation of the naphthalene system with the exploitation of the dicyanovinyl moiety of 2-naphthylalkylidenemalonodinitriles as an active electrophile in cold solutions of concentrated sulfuric acid. 2-(2-Naphthyl)propanal (), 1-(2-naphthyl)propan-2-one (), 3-(2-naphthyl)butan-2-one (), and 3-(2-naphthyl)pentan-2-one () had been condensed with malonodinitrile to afford 2-naphthylalkylidenemalonodinitriles which were then cyclised to give 4-amino-1-methylphenanthrene-3-carbonitrile (), 4-amino-2-methylphenanthrene-3-carbonitrile (), 4-amino-1,2-dimethylphenanthrene-3-carbonitrile (), and 4-amino-1-ethyl-2-metylphenanthrene-3-carbonitrile (). The nitrile function has been removed from the aminonitriles, with the exception of , through hydrolysis and decarboxylation in alkaline ethanolic solutions under elevated pressure (∼3 MPa) and temperature 220–230°C to give the respective 4-amino-methylphenanthrenes. Diazotisation of the phenanthreneamines and the reaction with hypophosphorus acid has lead to the methylphenanthrenes in moderate yields (50–52%).