Synthesis and Photophysical Study of Heteropolycyclic and Carbazole Motif: Nickel-Catalyzed Chelate-Assisted Cascade C–H Activations/Annulations

Abstract

Herein, nickel-catalyzed synthesis of polyarylcarbazole through sequential C–H bond activations has been described. Regioselective indole C2/C3 functionalization has been achieved in the presence of indole C7-H, which is quite challenging. In addition, this approach also gives easy access to building a heteropolycyclic motif through C6/C7 C–H functionalization of indoline. This methodology is not limited to aromatic internal alkynes as coupling partners; aliphatic alkynes have also shown good tolerance. Notably, during the optimization the catalytic enhancement with sodium iodide as an additive has been observed. We have also studied the photophysical properties of these highly conjugated molecules.

Multiple annulations of inert C(sp2)–H bonds with alkynes

“…Recently, the Kim and Ravikumar groups developed an ‘N’-directed similar kind of homologation of hetero(arenes) under Cp*Rh( iii ) [ 126 → 127 ] and Ni( ii ) [ 128 → 129 and 130 ] catalysts (Scheme 33E-F). 76…”

Diverse reactivity of alkynes in C–H activation reactions

“…Furthermore, in 2021 Ravikumar et al demonstrated the synthesis of poly-heterocyclic indoline 184 and bioactive carbazole motifs 186 via sequential C–H bond activation of indoline 183 and indole 185 using alkynes 182 (Scheme 61). 72 This selective functionalisation of indole, even in the presence of C7–H, makes this approach unique. The reaction conditions were optimized, following which the scope of the reaction was examined.…”

Reactivity of Alkynes with M-C Bonds generated through C-H Activation

“…An unwanted [2+2+2] cycloaddition reaction was observed for alkylsubstituted ynamides, thus giving lower yields. 71 This selective functionalization of indole, even in the presence of C7-H, makes this approach unique. The reaction condition was optimized, following which the scope of the reaction was examined.…”