Synthesis of New Pyrroline Nitroxides with Ethynyl Functional Group

3-Substituted and 3,4-disubstituted pyrroline nitroxides containing an ethynyl group or two ethynyl groups were achieved by the reaction of a paramagnetic aldehydes with dimethyl (1-diazo-2-oxopropyl)phosphonate (Bestmann-Ohira reagent). The new compounds containing an ethynyl group were found to be useful building blocks in Sonogashira coupling, cyclization, and cycloaddition reactions producing potentially azido-specific cross-linking spin labels, paramagnetic ligands, and polyradical scaffolds.