Microwave-Assisted Cycloaddition of Diisopropyl Diazomethylphosphonate to Electron-Deficient Alkenes: Synthesis of Multifunctionalized Phosphonopyrazolynes and Phosphonopyrazoles

An efficient method for the synthesis of functionalized phosphonopyrazolines has been developed. The procedure involved the microwave-assisted cycloaddition of diisopropyl diazomethylphosphonate to dipolarophiles, such as ex,alpha,beta-unsaturated-nitriles and -esters, performed in neat conditions. By oxidative aromatization the phosphonopyrazolines, thus obtained, were converted into the corresponding phosphonopyazoles Alternatively, phosphonopyazoles could be obtained by a one-pot, two step procedure directly from dipolarophiles, thus avoiding the isolation of the intermediate pyrazolines. Full spectroscopic characterization of the compounds has been also reported. (C) 2014 Elsevier Ltd. All rights reserved.