Click Triazole Directed C-H Activation And Its Applications In Organic Synthesis

The direct C-H functionalization has attracted considerable attention in recent years since it possess many advantages compared to traditional strategies, such as using cheap and readily available starting material, simplified synthetic procedure, higher atom efficiency, and less waste. In this paper, the preparation of PEG click triazole palladacycle and its application in palladium catalyzed cross-coupling in neat water is reported. The bidentate directing group directed palladium catalyzed sp2 C-H mono-methylation of triazolbenzamide is also included in this paper.The PEG-triazole-palladacycle were prepared through a “click” route in which the triazole was formed could act as both a linker and a chelator. The palladacycle was characterized by NMR and ICP-MS before being applied in aqueous cross-coupling. As a precatalyst, the palladacycle exhibited superior catalytic activity towards Suzuki-Miyaura cross-couplings. With only 0.005mol%-0.00005mol% catalyst loading, the reaction of arylbromides and phenylboronic could give good to high yields with the TONs of up to 9.8*105. After removing the products by simple extraction, the catalyst could be reused for 3 times without significant loss of activity. Furthermore, the palladacycle was also capable for copper-free aqueous Sonogashira cross-coupling re-actions with no homocoupling by-product being detected.The bidentate directing group directed palladium catalyzed sp2 C-H mono-methoxylation of triazolbenzamide has also been developed. Using Pd(OAc)2 as catalyst, PhI(CF3COO)2 as oxidant, MeOH as methoxylation reagent, the o-methoxylation of substrates were achieved in high yields. Additionally, the directing group could be removed in MeOH with BF3Et2 O under reflux.