Chemoselective aminomethylation of bifunctional substrates: carbonyl versus phenolic hydroxyl, carbonyl versus pyrazole and pyrrole versus phenolic hydroxyl as competing activating groups

2-Naphthol-pyrazole conjugates as substrates in the Mannich reaction

Several novel 2-naphthol-pyrazole conjugates have been synthesized through the O-alkylation of 1-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]naphthalen-2-ol with methyl iodide, benzyl chloride, methyl bromoacetate and N-benzyl-2-bromoacetamide. The aminomethylation of these 2-naphthol-pyrazole conjugates has been examined employing the classical conditions for the Mannich reaction, and also by using N,N-dimethylmethyleneiminium chloride as preformed aminomethylating reagent. In both situations, aminomethylation of these substrates occurred at C-4 of the pyrazole ring. The bifunctional substrate 1-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]naphthalen-2-ol has been chemoselectively aminomethylated in the pyrazole ring using the same preformed aminomethylating reagent.