Chemoselective Synthesis of 5-Alkylamino-1H-pyrazole-4-carbaldehydes by Cesium- and Copper-Mediated Amination

Article abstract of DOI:10.1002/ejoc.201500505

Microwave-assisted synthesis of new 5-alkylamino-pyrazole-4-carbaldehydes was performed efficiently, with yields up to 99 and short reaction times. Nucleophilic substitution of primary alkylamines with activated 5-chloro-1-(2-pyridyl)pyrazole-4-carbaldehyde was mediated by the "cesium effect". The amination of deactivated 1-aryl-5-chloropyrazole-4-carbaldehydes was also assisted by the cesium ion and catalyzed by copper(I). Hereby is described an efficient protocol for the chemoselective synthesis of new 5-alkylaminopyrazole-4-carbaldehydes from 5-chloropyrazole-4-carbaldehydes and primary alkylamines in one step to give products with good to excellent yields and short reaction times. Unexpectedly, under these reaction conditions the corresponding alkylimine formation was not observed.