A new class of bidentate ligands
was prepared by a modular approach
involving Rh-catalyzed C–H annulation reactions. The resulting
conformationally constrained ligands enabled the Pd-catalyzed C–H
alkenylation at electron-rich and sterically less hindered positions
of electron-rich arenes while promoting the facile oxidation of Pd(0)
intermediates by oxygen. This newly introduced ligand class is complementary
to the ligands developed for Pd-catalyzed oxidative reactions and
may find broad application in transition-metal-catalyzed reactions.
Modular approaches, which allow a systematic variation of heteroaromatic cores and substituents, are crucial for the development of heteroaromatic drug candidates and organic functional materials. A new strategy involving the cyclization of heteroarenes tethered with alkynes through a norbornene bridge was developed. The precursors were readily prepared by a three‐component coupling process of heteroaryl halides, norbornadiene, and terminal alkynes. The Pd catalytic system derived from Pd(OAc)2 and 2‐(pyrazol‐1‐yl)pyridine transformed a variety of five‐membered heteroarenes to the corresponding benzofused products, including (di)benzothiophene, indazole, carbazole, indole, and benzofuran, with aryl and alkyl substituents at the C4(C7) position. During the cyclization process, the norbornene ring underwent a retro‐Diels‐Alder reaction, serving as an acetylene synthon. This approach was used to synthesize naphthalene derivatives from electron‐rich arenes, demonstrating its versatility in the annulation of (hetero)aromatic rings.
Pd-catalyzed C–H alkenylations targeting the least hindered position of N-alkyl pyrroles and 3-substituted thiophenes, as opposed to electronically controlled approaches, are developed. The steric demand and stable bidentate binding mode...
This review describes recent advances in transition-metal-catalyzed C–H functionalization reactions of pyrazoles to form new C–C bonds on the pyrazole ring. In contrast to traditional cross-coupling reactions that require pre-functionalized...
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