Facile syntheses of 3,4-disubstituted pyrroline nitroxides and their further synthetic applications

Abstract

Lithiation of an α,β-unsaturated pyrroline nitroxide ester at the β-carbon with LTMP followed by treatment with electrophiles led to a new series of 3,4-disubstituted pyrroline nitroxides, which could be used as valuable paramagnetic building blocks. The new compounds were tested in Sonogashira and Stille cross coupling reactions, which offered methyl 1-oxyl-4-substituted-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-carboxylate radicals for new C–C bond formation in poor to moderate yields. The reaction of an α,β-unsaturated pyrroline nitroxide ester with methyl chloroformate generated diester 2b; the partial hydrolysis product of this reaction was shown to be a key compound for the synthesis of paramagnetic uracil derivative 10.