Reactions of HDDA Benzynes with C,N‐Diarylimines (ArCH=NAr')

• Published in: European journal of organic chemistry 2020-05, Vol.2020 (16), p.2379-2383
• Main Authors: Arora, Sahil, Sneddon, Dorian S., Hoye, Thomas R.
• Format: Article
• Language: English
• Subjects: Acridines; Azoquinone methides; Benzazetidines; Chemical synthesis; Cycloaddition; Dihydroacridines; HDDA‐benzynes; Imines; Manganese dioxide
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201901855

o‐Benzynes can be utilized to construct heterocyclic motifs using various nucleophilic and cycloaddition trapping reactions. Acridines have been synthesized by capture of C,N‐diarylimines with benzynes generated by classical methods (i.e., from ortho‐elimination of precursor arene compounds), although in poor yields. We report here that these imines can be trapped by benzynes generated by the hexadehydro‐Diels–Alder (HDDA) reaction in an efficient manner to produce 1,4‐dihydroacridine products. These dihydroacridines were subsequently aromatized using MnO2 to provide structurally complex acridines. Benzynes generated by the hexadehydro‐Diels–Alder (HDDA) reaction are shown to capture C,N‐diarylimines to produce 1,4‐dihydroacridine products. The reaction is thought to proceed via benzazetidine intermediates that then undergo electrocyclic ring‐opening and ‐closing (and rearomatization) to give the dihydroacridines. These were easily oxidized with MnO2 to provide structurally complex acridines.