Synthesis and reactions of some nitrone derivatives

Article abstract of DOI:10.1016/S0040-4020(96)01081-2

Arylnitroso compounds easily react as nucleophiles with conjugated azoalkenes to give α-(arylimino-N-oxide)hydrazones by their 1,4-addition to the azo-ene system. These adducts undergo an internal heterocyclization process with pyrazole ring formation to produce 1-alkoxycarbonyl- or 1-aminocarbonyl-3-methyl-4-(arylimino-N-oxide)-1H-pyrazol-5(4H)-ones stereoselectively in Z form by loss of an alcohol molecule. Deoxygenation of these compounds with triphenylphosphine affords 1-alkoxycarbonyl- or 1-aminocarbonyl-3-methyl-4-arylimino-1H-pyrazol-5(4H)-ones. Basic treatment with triethylamine of the same compounds leads to 3-methyl-4-(arylimino-N-oxide)-1H-pyrazol-5(4H)-ones by removal of the substituents on N(1) heteroatom of the pyrazole ring. Both deoxygenation and basic treatment of 1-alkoxycarbonyl- and 1-aminocarbonyl-3-methyl-4-(arylimino-N-oxide)-1H-pyrazol-5(4H)-ones have been realized sequentially, providing 3-methyl-4-arylimino-1H-pyrazol-5(4H)-ones. The same products were successfully obtained by reversing the order of these processes.