Synthesis of 5,6-dihydrobenz[c]acridines: a comparative study

5,6-Dihydrobenz[c]acridines were synthesized by the reaction of 1-chloro-3,4-dihydro-2-naphthaldehyde with aromatic amines under three different conditions: a. Thermolysis of 1-chlorovinyl-(N-aryl)imines prepared from 1-chloro-3,4-dihydro-2-naphthaldehyde. b. Acid catalyzed cyclization of 1-(N-aryl)amino-3,4-dihydro-2-naphthaldehydes. c. Thermolysis of N-arylenaminoimine hydrochlorides derived from 1-chloro-3,4-dihydro-2-naphthaldehyde in DMF medium. All the three approaches exclusively yielded only 5,6-dihydrobenz[c]acridines and not the isomeric 7,8-dihydrobenzo[k]phenanthridines. The structures of these products have been unambiguously established by detailed NMR spectral study and by independent synthesis as well as by single crystal XRD study.