3 years ago

Ligand-controlled Regiodivergent C−H Alkenylation of Pyrazoles and its Application to the Synthesis of Indazoles

Ho Ryu, Og Soon Kim, Jung Min Joo, Geunhee Kang, Hyun Tae Kim, Mu-Hyun Baik, Sang Min Lim, Abul Kalam Biswas, Hyeri Ha
Regioselective C4-, C5-, and di-alkenylation of pyrazoles was achieved. Electrophilic Pd catalyst generated by TFA and 4,5-diazafluoren-9-one (DAF) led to C4-alkenylation, whereas KOAc and mono-protected amino acid (MPAA) ligand, Ac−Val−OH gave C5-alkenylation. Combining palladium acetate with silver carbonate and pivalic acid, dialkenylation products were formed. Annulation via sequential alkenylation, thermal 6π-electrocyclization, and oxidation gave functionalized indazoles. This comprehensive strategy greatly expanded the range of readily accessible pyrazole and indazole derivatives, enabling useful regiodivergent C−H functionalization of pyrazoles and other heteroaromatic systems.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201709162

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