C−H Alkenylation of Pyrroles by Electronically Matching Ligand Control

• Published in: Chemistry, an Asian journal an Asian journal, 2018-09, Vol.13 (17), p.2418-2422
• Main Authors: Kim, Hyun Tae, Lee, Woohyeong, Kim, Eunmin, Joo, Jung Min
• Format: Article
• Language: English
• Subjects: Alkenes; alkenylation; Catalysis; Catalysts; Chemistry; Ligands; Palladium; Pyrroles; Substrates
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201800558

Directing group and substrate control strategies have frequently been employed for the regioselective C−H alkenylation of acid‐ and oxidant‐sensitive pyrrole heterocycles. We developed an undirected, aerobic strategy for the C−H alkenylation of N‐alkylpyrroles by ligand control. For C2‐alkenylation of electron‐rich N‐alkylpyrroles, an electrophilic palladium catalyst derived from Pd(OAc)2 and 4,5‐diazafluoren‐9‐one (DAF) was used. Alternatively, a combination of Pd(OAc)2 and a mono‐protected amino acid ligand, Ac‐Val‐OH, was useful for C5‐alkenylation of N‐alkylpyrroles possessing electron‐withdrawing groups at the C2 position. This approach based on the electronic effects of heterocycles and catalysts can rapidly provide a wide range of alkenyl pyrroles from readily available N‐alkylpyrroles and alkenes. In control! Depending on the electronic character of pyrroles, matching palladium catalytic systems were developed for a regioselective C−H alkenylation. Complementary to directing group and substrate control strategies, this approach based on electronic matching between heterocycles and catalytic systems should be useful for providing a variety of alkenyl pyrroles from readily available N‐alkylpyrroles and alkenes.