Abstract

3-Phenyl-5-pyrazolone (1) is selectively alkylated at position 1 in 40% yield. The alkylated compound (2) is acylated (3) in 60% yield and nitrosated (4) in 80% yield. According to the spectroscopic data a N-H or O-H structure can be proposed for 1 in DMSO. The proton may be at N-2 or on the oxygen at C-5, respectively. The alkylated compound 2 exists as 5-pyrazolone in chloroform with a CH2 at C-4. In DMSO, 2 is a 5-hydroxypyrazole. For compound 3 in chloroform the structure corresponds to 4-acyl-5-hydroxypyrazole. For compound 4 in chloroform there is one tautomer with a 4-nitroso-5-hydroxypyrazole structure while in DMSO the same 4-nitroso-5-hydroxypyrazole (92%) and a 4-nitroso-5-pyrazolone (8%) tautomer can be found