A convenient and highly efficient palladium‐catalyzed direct C2‐arylation/heteroarylation of N‐substituted benzimidazole derivatives such as N‐benzyl/3‐chlorobenzyl/2,4,6‐trimethylbenzyl/2,4,6‐triisopropylbenzyl/aryl benzimidazoles with various aryl/heteroaryl bromides in the presence of Pd–PEPPSI (palladium‐pyridine enhanced pre‐catalyst preparation stabilization and initiation) complexes is reported. In order to that we have prepared a series of different symmetrical and unsymmetrical N,N′‐diaralkyl benzimidazole‐bearing Pd–PEPPSI complexes. Among all of the the prepared complexes, Pd–PEPPSI‐3 effectively tuned the reaction at a relatively higher rate under mild reaction conditions in an ethanol–water system. In addition, the catalytic process avoids the use of external ligand and additives. Further the reactivity was compared with commercially available copper‐N‐heterocyclic carbene catalyst, but the reaction was less successful. With the optimized reaction conditions, a wide range of 2‐aryl/heteroaryl‐N‐substituted benzimidazoles were synthesized in good to excellent yields via Csp2‐H/Csp2‐X biaryl cross‐coupling.

A protocol for the Suzuki–Miyaura coupling of novel 2‐(6‐chloropyridazin‐3‐yl)‐5‐(aryl/heteroarylsulfonyl)‐2,5‐diazabicyclo[2.2.1]heptanes and heteroarylboronic acids to afford variety of coupled products was realized. Pd‐PEPPSI‐IPr catalyst was found to be a powerful and reusable catalyst under relatively mild reaction conditions.

A series of new benzimidazolium chlorides bearing N,N′-benzyl, 2,4,6trimethylbenzyl and 2,4,6-triisopropylbenzyl substituents have been designed and synthesized from various o-phenylenediamines. Subsequently, corresponding Cu-based N-heterocyclic carbenes (NHCs) were generated in situ in the reaction medium which represents a new application of NHCs exploiting distinct catalytic property towards intermolecular cyclization reaction cascade for the synthesis of 2-aryl-3-(arylethynyl)quinoxalines from ophenylenediamines and terminal alkynes. The outcome of the cyclization reaction product depends upon the N,N′-substituents present on the benzimidazolium chlorides.

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Award Number: 02 (0248)/15/EMR-II2-Aryl/heteroaryl-substituted benzoxazoles are important heterocyclic motifs extensively found in several bioactive molecules, pharmaceuticals and natural products. In view of the importance of these compounds, there is need to develop easiest and simplest synthetic routes. The motive of this current work is to conduct the direct C2-arylation reaction on benzoxazole with various cross-coupling partners like aryl/heteroaryl halide/carboxylic acid/ diazonium tetrafluoroborate/sulfonyl chloride/boronic acids in the presence of different symmetrical and unsymmetrical Pd-PEPPSI (pyridine-enhanced pre-catalyst preparation by stabilization initiation) catalysts via C (sp 2 )-C (sp 2 ) bond formation. Compared with other coupling partners, boronic acids coupled with benzoxazole very efficiently in the presence of sterically and electronically tunable bulky1,3-bis(N,N 0 -2,4,6-triisopropylbenzyl) benzimidazolium-Pd-PEPPSI complex in open air to offer the corresponding C2-aryl/heteroaryl benzoxazole compounds. Further, it is worthy to mention that there is no need of any external oxidant/ligand/additive for the complete conversion of starting molecules to products. The reactions progressed successfully with a wide range of substrate scope and attained the products in good to excellent yields in a short reaction time in ethanol/ water (1:1) medium. Greatly, catalysts can be recovered and reused for few cycles with significant reactivity.