The contrasting reactivity of trans - vs. cis -azobenzenes (ArNNAr) with benzynes

• Published in: Chemical science (Cambridge) Vol. 14; no. 24; pp. 6730 - 6737
• Main Authors: Sneddon, Dorian S., Hoye, Thomas R.
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 21.06.2023; Royal Society of Chemistry; The Royal Society of Chemistry
• Subjects: Azo compounds; Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Ring opening; Science & Technology; 3,5-CYCLOHEXADIENE-1,2-DIIMINE
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/D3SC02253F

We report here a study that has revealed two distinct modes of reactivity of azobenzene derivatives (ArNNAr) with benzynes, depending on whether the aryne reacts with a trans - or a cis -azobenzene geometric isomer. Under thermal conditions, trans -azobenzenes engage benzyne via an initial [2 + 2] trapping event, a process analogous to known reactions of benzynes with diarylimines (ArCNAr). This is followed by an electrocyclic ring opening/closing sequence to furnish dihydrophenazine derivatives, subjects of contemporary interest in other fields ( e.g. , electronic and photonic materials). In contrast, when the benzyne is attacked by a cis -azobenzene, formation of aminocarbazole derivatives occurs via an alternative, net (3 + 2) pathway. We have explored these complementary orthogonal processes both experimentally and computationally.