Bromination of Phenalenone and 2-Aminophenalenone

Abstract

Bromination of phenalenone C 1 J or 2-bromophenalenone [2] gave 2, 6-dibromophenalenone C 3 D. The substitution at 6-position, which had long been accepted without conclusive evidence, was confirmed by the NMR spectrum and oxidative degradation of C 31 2, 6, 8-Tribromophenalenone C 4 j was obtained from Cl J by bromination in nitrobenzene at 80400° C in the presence of iodine and iron powder. The oxidation of C 4 J afforded 3, 5-dibromonaphthalic anhydride. When Cl J was brominated in boiling bromine by using iodine as a catalyst, 2, 6, 7, 8-tetrabromophenalenone C 5 J was obtained. The compound C5 J was oxidized to 3, 4, 5- tribromonaphthalic anhydride [15].
2-Aminophenalenone was brominated to 2-amino-3-bromo-[l0] and 2-amino-3, 6-dibromophenalenone C.11D by one and two moles of bromine, respectively. The latter compound was also obtained from 2-amino-6 -bromophenalenone [9].
The electronic spectra of phenalenones Cl-[5] and their conjugate acids CI c-[5 c] showed parallel spectral shifts according to the number of bromine atoms, with exception of a set of C 5 D and [5]. For [5] and [5], the deviation from the relationship can be attributed to steric effect of three neighboring substituents.