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

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

Author(s): Hyun Tae Kim; Hyeri Ha; Geunhee Kang; Og Soon Kim; Ho Ryu; Abul Kalam Biswas; Sang Min Lim; Mu-Hyun Baik; Jung Min Joo

Subject: alkenylation, ; C-H activation, ; indazole, ; palladium, ; pyrazole

Journal: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, v.56, no.51, pp.16262 - 16266

Abstract: Regioselective C4-, C5-, and di-alkenylations of pyrazoles were achieved. An electrophilic Pd catalyst generated by trifluoroacetic acid (TFA) and 4,5-diazafluoren-9-one (DAF) leads to C4-alkenylation, whereas KOAc and mono-protected amino acid (MPAA) ligand Ac-Val-OH give C5-alkenylation. A combination of palladium acetate, silver carbonate, and pivalic acid affords dialkenylation products. Annulation through sequential alkenylation, thermal 6 pi-electrocyclization, and oxidation gives functionalized indazoles. This comprehensive strategy greatly expands the range of readily accessible pyrazole and indazole derivatives, enabling useful regiodivergent C-H functionalization of pyrazoles and other heteroaromatic systems (c) 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim