title: Base-catalyzed synthesis of substituted indazoles under mild, transition-metal-free conditions.
abstract: Back to basics: A transition-metal-free method developed for the synthesis of indazoles involves an inexpensive catalytic system composed of a diamine and K2CO3. Various (Z)-2-bromoacetophenone tosylhydrazones were converted into indazoles at room temperature in excellent yields (see example; Ts = p-toluenesulfonyl). The yield was improved by photoisomerization with UV light when E/Z isomeric mixtures of the starting material were used.
authors.affiliation: Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52056 Aachen, Germany.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Thomé
authors.forename: Claire
authors.initials: C
authors.lastname: Besson
authors.forename: Tillmann
authors.initials: T
authors.lastname: Kleine
authors.forename: Carsten
authors.initials: C
authors.lastname: Bolm
keywords: N-arylation; heterocycles; hydrazones; indazoles; synthetic methods