External Oxidant-Dependent Reactivity Switch in Copper-Mediated Intramolecular Carboamination of Alkynes: Access to a Different Class of Fluorescent Ionic Nitrogen-Doped Polycyclic Aromatic Hydrocarbons

Abstract

An interesting case of external oxidant-controlled reactivity switch leading to a divergent set of ionic nitrogen-doped polycyclic aromatic hydrocarbons (N-doped PAHs), is presented here, which is quite unrecognized in copper-mediated reactions. In the current scenario, from the same pyridino-alkyne substrates, the use of the external oxidant PhI­(OAc)2, in combination with Cu­(OTf)2, gave N-doped spiro-PAHs via a dearomative 1,2-carboamination process; whereas, without the use of oxidant, an alkyne/azadiene [4 + 2]-cycloaddition cascade occurred to exclusively afford ionic N-doped PAHs. These newly synthesized N-doped PAHs further exhibit tunable emissions, as well as excellent quantum efficiencies.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…It was later found that the outcome of the reaction depends on the oxidant; in particular, the use of a hypervalent iodine reagent led to spirocyclized products. 516 …”

1,2-Difunctionalizations of alkynes entailing concomitant C–C and C–N bond-forming carboamination reactions

“…Interestingly, the use of oxidant PhI(OAc) 2 as an additive offered a completely different product 111 ( Scheme 63 ). 76 The reaction offered access to variously substituted PAHs. Interestingly, aliphatic alkynes did not produce the desired 111, but 110 was obtained in good yield.…”

1,2‐Aminofunctionalization Reactions of Pyridino‐Alkynes via Carbophilic Activation

“…). [41] Thus, based on an "optimization-on-observation" approach, an oxidant-controlled reactivity switch has been achieved on these pyridinoalkyne cores. To the best of our knowledge, this reaction represents the first example of intramolecular dearomative 1,2carboamination of alkynes utilizing oxidative copper chemistry.…”

“…In our continuing research on realizing 1,2-aminofunctionalization reactions of pyridino-alkynes, a diverse synthetic potential of these cores was discovered based on their reactivity switch in presence of different metal catalysts. While working on the optimization of our initial project regarding Cu(OTf) 2mediated 1,2-carboamination reaction of 2-phenyl-6-(2-alkynylphenyl)pyridine skeletons (41) for the synthesis of PAHs 42 (Scheme 13), [39] formation of pyrido-isoquinoline salts 64 was encountered during the screening of silver catalysts. An AgOTf-mediated hydroamination reaction of 63 has successfully led to access 64 (Scheme 22).…”

“…With an aim to optimize such result, we have established a reaction condition where the use of 1.5 equivalent of external oxidant PhI(OAc) 2 (PIDA) in combination with 1 equivalent of Cu(OTf) 2 successfully afforded 46 via a dearomative 1,2‐carboamination process from the pyridino‐alkyne substrates 45 (Scheme 16). [41] Thus, based on an “optimization‐on‐observation” approach, an oxidant‐controlled reactivity switch has been achieved on these pyridino‐alkyne cores. To the best of our knowledge, this reaction represents the first example of intramolecular dearomative 1,2‐carboamination of alkynes utilizing oxidative copper chemistry.…”