No abstract

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 simple and efficient synthesis of a series of unexisting Pd-PEPPSI complexes is summarized. These complexes are exploited for their high catalytic activity towards Buchwald–Hartwig amination.

A new diversified, rapid and easily accessible, N‐heterocyclic carbene based palladacycle, SingaCycleTM‐A1 exploited for the cross coupling reactions on heterocyclic amines. This Pd‐NHC catalyst is considered to be merely stable and takes part in dynamic conversion of various organic functionalities. Herein, we report its first time use in the synthesis of C‐ and N‐ diaryl/ heteroaryl pyridine analogues from the less active parent 5‐bromopyridine‐2‐amine via sequential Suzuki‐Miyaura and Buchwald couplings. Surprisingly, both the coupling reactions proceed very smoothly and efficiently under mild reaction conditions in green solvent system (ethanol:water) at a faster rate. Moreover 1 mol% of the catalyst is sufficient to proceed the reactions and obtain comparatively better results.

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.