Nitration of 9,10-Dialkylphenanthrenes. Side-chain Nitrooxylation in Competition with Side-chain Nitration

Abstract 9,10-Dimethylphenanthrene and 9-methyl-10-ethylphenanthrene gave 9-methyl-10-nitromethylphenanthrene and 9-ethyl-10-nitromethylphenanthrene, respectively, as major product, when treated with fuming nitric acid in dichloromethane at low temperatures. In contrast, 9,10-diethylphenanthrene yielded a comparable mixture of products arising from side-chain nitration and side-chain nitrooxylation, which on chromatography over deactivated alumina gave 9-ethyl-10-(α-nitroethyl)phenanthrene and 9-ethyl-10-(α-hydroxyethyl)phenanthrene as main isolable products. 9-Methylphenanthrene and 9-ethylphenanthrene were both simply nitrated at the ring position to give the corresponding 9-alkyl-10-nitrophenanthrenes in good yields. No side-chain attack was observed. Factors responsible for determining which one of the competitive pathways will be followed have been discussed.