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.