Nitrosation of 1,3-Diarylureas with Nitrosyl Chloride, Dinitrogen Trioxide and Dinitrogen Tetroxide in Dimethylformamide

Nitrosation of 1,3-diarylureas (Ia-f) with nitrosyl chloride or dinitrogen trioxide in dimethylformamide gave 1,3-diaryl-1-nitrosoureas (IIa-f) in 59-96% yields, and nitrosation of 1,3-diarylureas (Ia, c-f) with dinitrogen tetroxide also gave 1,3-diaryl-1-nitrosoureas (IIa, c-f) in 75-91% yields. However, nitrosation of 1,3-bis (4-methoxyphenyl) urea (Ib) with dinitrogen tetroxide in dimethylformamide resulted in the formation of 1-(4-methoxy-2-nitrophenyl)-3-(4-methoxyphenyl) urea (III) in 60% yield, and nitrosation with a large excess of dinitrogen tetroxide gave 1,3-bis (4-methoxy-2-nitrophenyl) urea (IV) in 42% yield.