Synthesis of cycloalka[a]- and cycloalka[c]phenanthrene aminonitriles from2-(1-naphtyl)cycloalkylidene malonodinitriles involving novel aromatic rearrangement

Cyclization of 2-(1-naphthyl)cyclopentylidene malono-dinitrile (2a) in poly phosphoric acid (PPA) affords 5-amino-2,3-dihydro-1H-cyclopenta[c]phenanthr ene-4-carbonitrile (4a), a product of straightforward cyclization, and 11-a mino-16,17-dihydro-15H-cyclopenta[a]phenanthrene-12-carbonitrile (3a), whic h appears to result through rearrangement of the carbon framework of 2a. Ri ng closure of 2-(1-naphthyl)cyclohexylidenemalonodinitrile (2b) or ethyl 2- (1-naphthyl)cyclopentylidenecyanoacetate (2c) in concentrated sulfuric acid or PPA give nearly exclusively the following rearranged products: 5-amino- 7,8,9,10-tetrahydrochrysene-6-carbonitrile (3b) or ethyl 11-amino-16,17-dih ydro-15H-cyclopenta[a]phenanthrene-12-carboxylate (3c), respectively. Amino nitriles 3a and 4a are obtained as an easily separable mixture in 58:42 rat io. A suggested mechanism of this new aromatic rearrangement is presented.