Naphth[1,2‐d]oxazole intermediates in the preparation of 3‐hydroxy‐4‐(1‐alkyl‐3‐methyl‐5‐hydroxy‐4‐pyrazolyl)‐azo‐1‐naphthalenesulfonamide dyes

Acylation of 4-amino-3-hydroxy-1-naphthalenesulfonic acid (3) with benzoyl chloride in pyridine gave pyridinium 3-hydroxy-4-(N-benzoylamino)-1-naphthalenesulfonate (12) which was converted by thionyl chloride followed by diethylamine into N,N-diethyl-2-phenylnaphth[1,2-d]oxazole-5-sulfonamide (14). The naphthoxazole moiety was hydrolyzed with potassium hydroxide and the resulting N,N-diethyl-4-amino-3-hydroxy-1-naphthalenesulfonamide (11) coupled with 1-alkyl-3-methyl-5-pyrazolones. The 2-phenylnaphth[1,2-d]oxazole intermediates and various by-products were investigated.