Synthesis of trisubstituted thiazoles by ligand-free palladium-catalyzed direct 5-arylation of 2,4-disubstituted thiazoles under conventional and microwave-assisted heating

Trisubstituted thiazoles were synthesized with excellent yields using ligand-free, palladium-catalyzed, direct 5-arylation of 2,4-disubstituted thiazole and conventional or microwave-assisted heating. The palladium-catalyzed reaction yields were significantly influenced by LiCl additive, solvent, and heating method. The reaction times were reduced dramatically by employing microwave radiation instead of conventional heating. The synthetic methods can be applied to diverse 2,4,5-trisubstituted thiazoles by varying the aryl bromide and disubstituted thiazole reactants.     

Synthesis of 1,4-diarylsubstituted 1,3-diynes through ligand-free copper-catalyzed oxidative decarboxylative homocoupling of aryl propiolic acids

An efficient method of ligand-free Cu-catalyzed oxidative decarboxylative homocoupling of aryl propiolic acids was developed. When CuI was employed as the catalyst and I₂ as the oxidant, the decarboxylative homocoupling reaction for C_sp–C_sp bond formation in DMSO underwent smoothly to afford the corresponding 1,4-disubstituted 1,3-dialkynes in good to excellent yields without any organic ligands. This catalytic system was applicable to aryl propiolic acids bearing different steric, electronic, and functional groups.     

纯水中有氧条件下Pd/C催化的无配体Suzuki反应简

报道一种在纯水中Pd/C催化的高效Suzuki反应体系,该体系无需除氧,且无外加配体和添加剂,底物普适性广泛,含有亲水或疏水基团的溴代芳烃都能被高效活化. 此外,对部分杂环芳烃与芳基硼酸的偶联反应也有较好的催化效果. 该催化剂可高效循环使用三次,且性能无明显下降.     

Palladium(0) nanoparticles-catalyzed ligand-free direct arylation of benzothiazole via C-H bond functionalization

Palladium nanoparticles, generated in situ efficiently catalyzes direct 2-C-H arylation of benzothiazole without requirement of any ligand. A wide range of substituted aryl and heteroaryl iodides participate in this reaction producing a series of 2-aryl/heteroaryl-benzothiazoles in high yields.     

An efficient and simple protocol for a PdCl2-ligandless and additive-free Suzuki coupling reaction of aryl bromides

A highly efficient, convenient, and environmentally friendly protocol was developed for the PdCl₂-catalyzed ligandless and additive-free Suzuki reaction of aryl bromides with arylboronic acids in water/ethanol.     

Pd-nanoparticles catalyzed denitrogenative coupling of aryl halides with arylhydrazines: Greener approach for biaryls synthesis under ligand-free condition

The greener approach for the synthesis of biaryl using palladium nanoparticle (Pd–NPs) catalyzed denitrogenative coupling between aryl hydrazine and aryl halides under ligand-free condition has been described. The phytochemicals of the black pepper extract plays a dual role in reduction of Pd^II to Pd⁰ and acts as stabilizing agent for Pd–NPs. The electronically diver's arylhydrazines and commercially available aryl halides are used for the synthesis of symmetrical and unsymmetrical biaryls in good to excellent yield. The mechanism is well supported by control experiment and the recyclability, turnover number and turnover frequency of biogenically synthesized Pd–NPs is studied.     

Substrate-promoted ligand-free CuI catalyzed S-arylation of 2-mercaptobenzothiazoles with aryl iodides in water

A green and efficient method has been developed for the cross-coupling of 2-mercaptobenzothiazoles with aryl iodides in water. The reactions proceeded smoothly under ligand-free conditions in the presence of TBAB to give the corresponding products in good yields. The protocol showed good tolerance toward a variety of functional groups. A substrate-promoted mechanism for this catalytic reaction has been proposed.     

Palladium on charcoal-catalyzed ligand-free Stille coupling

An efficient ligand-free Stille coupling reaction catalyzed by palladium on charcoal was developed. Tetraphenyltin was reacted with a variety of aryl halides including aryl chlorides using LiCl as an additive. The reactions of tributyl organotin compounds with aryl iodides were effectively expedited by the addition of LiF. These reactions efficiently proceeded without a phosphine or arsenic ligand and no leached palladium was detected in the reaction mixture.     

Ligand free copper-catalyzed N-arylation of heteroarylamines

An efficient protocol for ligand-free Cu-catalyzed N-arylation of heteroarylamines has been developed. With the use of 1% CuI, a wide range of aryl iodides and bromides coupled with heteroarylamines to afford the corresponding products in high yields. Further, this protocol is particularly suitable for reactions of the most hindered aryl iodides with 2-aminopyridines.     

Ligand-free palladium catalysed Heck reaction of methyl 2-acetamido acrylate and aryl bromides as key step in the synthesis of enantiopure substituted phenylalanines

A range of substituted aryl bromides were coupled with methyl 2-acetamido acrylate using ligand-free palladium catalysis. Subsequently asymmetric hydrogenation with Rh/MonoPhos yielded substituted phenylalanines in high enantioselectivities (e.e. 92-99%).