SYNTHESIS AND REACTIONS OF SOME NITRONE DERIVATIVES

Arylnitroso compounds easily react as nucleophiles with conjugated azo alkenes to give alpha-(arylimino-N-oxide)hydrazones by their 1,4-addit ion to the azo-ene system. These adducts undergo an internal heteroxyc lization process with pyrazole ring formation to produce 1-alkoxycarbo nyl- or methyl-4(arylimino-N-oxide)-1H-pyrazol-5(4H)-onses stereoselec tively in Z form by loss of an alcohol molecule. Deoxygenation of thes e compounds with triphenylphosphine affords 1-alkoxycarbonyl- or rbony l-3-methyl-4-arylimimo-1H-pyrazol-5(4H)-ones. Basic treatment with tri ethylamine of the same compounds leads to -methyl-4(arylimino-N-oxide) -1H-pyrazol-5(4H)-ones by removal of the substituents on N(1) heteroat om of the pyrazole ring. Both deoxygenation and basic treatment of 1-a lkoxycarbonyl- and methyl-4-(arylimino-N-oxide)-1H-pyrazol-5(4H)-ones have been realized sequentially, providing 3-methyl-4-arylimino-1H-pyr azol-5(4H)-ones. The same products were succesfully obtained by revers ing the order of these processes. (C) 1997, Elsevier Science Ltd.