Synthesis of Novel 7-Alkynylindazole Derivatives: Molecular and Crystal Structure of 7-(pent-1-ynyl)-1H-Indazole

Abstract

A facile synthesis of novel 7-alkynylindazole derivatives involving the Pd/C-PPh 3 -CuI catalysed Sonogashira coupling of 7-iodoindazole with a wide range of terminal alkynes in aqueous medium is reported. An X-ray crystallographic study established the molecular structure of 7-(pent-1-ynyl)-1H-indazole.

Direct Catalytic Functionalization of Indazole Derivatives

“…In this method, Sonogashira type cross-coupling of 7-iodo-1H-indazole (64 a) with terminal alkynes was occurred in presence of Pd/CÀ PPh 3 À CuI as a catalytic system and pyrrolidine as a base in H 2 O at 80°C for 2-3 hours to achieve corresponding C-7 alkynylated 1H-indazole products (64 b) (Scheme 64). [124] A wide number of terminal alkynes were easily taking part in this reaction and produced corresponding C-7 alkynylated products with moderate to good yields alkynylating agent in presence of 10 mol% of Pd (OAc) 2 as a catalyst, monoprotected 3-amino-2-hydroxypyridine/pyridone as ligand (65 b), LiF as an additive and Ag 2 CO 3 as a base and norbornene (methylbicyclo[2.2.1]hept-2-ene-2-carboxylate) (NBEÀ CO 2 Me) as a transient mediator in DCM at 100°C for 24 hours. The corresponding C-4 alkynylated indazole product (65 d) was obtained with 53% yield (Scheme 65).…”