Synthesis of 5-azapentacene by Friedländer reaction and its properties

Abstract

The Friedländer reaction of cyclohexanone with 3-aminoanthracene-2-carbaldehyde afforded corresponding 1,2,3,4-tetrahydronaphtho[2,3-b]acridine in 79%, which was also prepared by reduction of the alternative Friedländer adduct 1,2,3,4-tetrahydronaphtho[2,3-b]acridine-7,12-dione, in 56% yield. Dehydrogenation of 1,2,3,4-tetrahydronaphtho[2,3-b]acridine led to naphtha[2,3-b]acridine (5-azapentacene). 1,2,3,4-Tetrahydro-5-azapentacene and 5-azapentacene are somewhat unstable in solution while these compounds keep their identity in solid state a little longer period of time under inert gas in the refrigerator. The decomposition rate of 1,2,3,4-tetrahydro-5-azapentacene was determined by UV absorption spectra to afford a rate constant, 3.92×10−3 s−1 (R=0.982) while 5-azapentacene was too unstable to determine the decomposition rate constant.