Cross‐Coupling Reactions on Azoles with Two and More Heteroatoms

Abstract

Recent progress in the field of transition‐metal‐catalyzed cross‐coupling reactions on various azole systems is summarized. Most important C–C‐ and C–X‐bond formation methodologies (Negishi, Suzuki–Miyaura, Stille, Kumada–Corriu–Tamao, Hiyama, Sonogashira, Heck, C–H activation) are reviewed and discussed for the imidazole, oxazole, thiazole, pyrazole, isoxazole, and isothiazole system, as well as for azoles with more than two heteroatoms. This review covers the literature that appeared in the past ten years up to the end of 2005 with corresponding azoles used either as metal organyl or halide (including triflates and some other less frequently applied leaving groups); literature describing azole structures only as ligands was not included.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Synthesis of 3-substituted 1-phenyl-1H-pyrazole-4-carbaldehydes and the corresponding ethanones by Pd-catalysed cross-coupling reactions

“…2 A number of accordant studies on azoles with these reactions have been published. 3 These heteroarenes represent the prevalent substructures for a variety of target compounds, with applications ranging from pharmaceuticals to molecular organic materials. In particular, substituted pyrazoles (1,2-diazoles) are interesting building blocks and frequently encountered structural units in a variety of pharmaceuticals, manganese dioxide and subsequent catalytic debenzylation is reported in a patent application, neither a source of the starting material nor spectroscopic data of the products were provided.…”

“…The synthesis of carbaldehyde 10 was reported earlier by a two-step pyrazole ring formation from acetophenone and phenylhydrazine to produce acetophenone phenylhydrazone, followed by Vilsmeier-Haack reaction to give the target carbaldehyde 10, 26 which is widely used in the synthesis of biologically active molecules. 3 ] and the base [TEA, NEt(iPr) 2 ], did not result in a marked improvement of yield. The cross-coupled products 22-27 were obtained in an isomerically pure E-form after isolation and purification by column chromatography.…”

An efficient oxidation of 2-pyrazolines and isoxazolines by bis-bromine-1,4-diazabicyclo[2.2.2]octane complex (DABCO-Br2)

“…7 Recently, transition-metal catalyzed coupling-cyclization reaction of functionalized allenes with organic halides for synthesis of pyrazoles has been reported. 8 These facts substantiate an obvious demand for development of new synthetic methods for isoxazoles and pyrazoles due to their importance both as synthetic intermediates 9 and as pharmacological targets. 10 Isoxazoles and 2-pyrazoles can be easily obtained respectively from oxidation of isoxazolines 11,12 and 2-pyrazolines.…”

Mild and efficient oxidation of 2-pyrazolines and isoxazolines by trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane–NH4Cl–HOAc in water–MeCN

“…Several isoxazoles and pyrazoles have agrochemical herbicidal and soil fungicidal activity and act as pesticides and insecticides [7,8]. Isoxazoles and pyrazoles are also useful synthetic intermediates capable of undergoing a variety of transformations and transition-metal catalyzed cross-coupling reactions, for example Heck, Stille, Suzuki, Sonogashira, and Negishi coupling [9]. Isoxazoles and pyrazoles are also in demand because of their importance both as synthetic intermediates [10] and as pharmacological agents [11].…”