Synthesis of new 1‐[4‐methane(amino)sulfonylphenyl)]‐5‐[4‐(aminophenyl)]‐3‐trifluoromethyl‐1 H ‐pyrazoles

magnified image A regiospecific cyclization‐dehydration reaction of a 1‐[(4‐( N ‐alkyl‐ N ‐( tert ‐butyloxycarbony)amino)‐phenyl]‐4,4,4‐trifluorobutane‐1,3‐done with a 4‐aminosulfonyl‐, or 4‐methylsulfonyl‐, phenylhydrazine hydrochloride in refluxing ethanol proceeded with simultaneous loss of the N‐tert ‐butyloxycarbonyl protecting group to afford a group of 1‐(4‐methanesulfonylphenyl or 4‐aminosulfonylphenyl)‐5‐[4‐( N ‐alkylaminophenyl)]‐3‐(trifluoromethyl)‐11 H ‐pyrazoles(6). Subsequent reaction of the pyrazole 6 (R 1 = R 2 = Me) with nitric oxide (40 psi) proceeded via a N ‐methylamino‐ N ‐diazen‐1‐ium‐1,2‐diolate intermediate that undergoes protonation of the more basic diazen‐1‐ium‐1,2‐diolate N 2 ‐nitrogen and then loss of a nitroxyl (HNO) species to furnish the N ‐nitroso product 7.