Rhodium(III)‐Catalyzed Annulation of 2‐Arylimidazo[1,2‐a]pyridines with Maleimides: Synthesis of 1H‐Benzo[e]pyrido[1′,2′:1,2]imidazo[4,5‐g]isoindole‐1,3(2H)‐Diones and their Photophysical Studies

Abstract

Rhodium(III)-catalyzed dehydrogenative annulation of 2-aryl-imidazo[1,2-a]pyridines with maleimides is described. The reaction afforded 1H-benzo[e]pyrido[1',2':1,2]imidazo[4,5-g]isoindole-1,3(2H)-diones in high yields with wide range of functional group tolerance. The reaction proceeds through Rh(III)-catalyzed CÀ H bond activation, followed by maleimide insertion and intramolecular cyclization. Photophysical properties of 1H-benzo[e]pyrido[1',2':1,2]imidazo[4,5-g]isoindole-1,3(2H)-diones were studied with UVvisible and fluorescence spectroscopy and validated by quantum chemical calculations. All the annulated products showed large Stokes shift values with emission in the range of 530-618 nm, and moderate to high quantum yields.

Competition between Two Modes of 6π‐Photocyclization: A Case Study for 3‐(1,2‐Diarylvinyl)‐2‐arylimidazo[1,2‐a]pyridines

“…Naphtho[1',2':4,5]imidazo[1,2-a]pyridine derivatives were established as efficient luminophores with intense fluorescence in the blue region. [42,43] Our products 3 also display strong emission both in toluene and acetonitrile with quantum yields of 0.20-0.60, while in toluene these values were greater. Figure 1 shows the fluorescence spectra of 3 a and pictures of its solutions under UV light.…”

Recent advances in transition-metal-catalyzed directed C–H alkenylation with maleimides

“…26 Almost at the same time, Kumar described the same transformation of dehydrogenative annulation of 2-aryl-imidazo[1,2- a ]pyridines with maleimides by taking Cu(OAc) 2 as oxidants (Scheme 8C). 27 In addition, they studied the absorption and emission spectra of all the annulated products indicating that these compounds might be used as emitting materials for OLED devices or biosensors. Recently, Kumar reported a operationally simple and scalable Rh( iii )-catalyzed dehydrogenative annulation and spirocyclization of 2-arylindoles/2-(1 H -pyrazol-1-yl)-1 H -indoles with maleimides (Scheme 8D).…”

Ortho C−H Functionalization of 2‐Arylimidazo[1,2‐a]pyridines

“…At around the same time, a dehydrogenative annulation of 2‐aryl‐imidazo[1,2‐ a ]pyridines 16 a was enlisted by the Kumar group [27] using Rh‐catalyst. Although, unlike the previous method, maleimides 16 b were used as an annulative substrate for this methodology.…”