Benzotriazoles, reductive acetylation

The hydroxyphenylbenzotriazole structure was constructed by a coupling of the diazonium salt of o-nitroaniline with 4-ethyl-phenol, followed by reduction of the nitro-azobenzene to the benzotriazole with zinc powder and NaOH. After blocking of the phenol by acetylation, bromination and dehydrobromination were performed as described earlier, and treatment with aqueous NaOH... 

A second synthesis for the preparation of 2H5V (29) starts by condensation of o-nitrobenzenediazonium chloride withT-hydroxyaceto-phenone. The azo compound was reduced with zinc and sodium hydroxide without reduction of the carbonyl group of the acetyl group. After acetylation, 2(2-acetoxy-5-acetylphenyl)2H-benzotriazole (2A5A) was reduced with sodium borohydride and the secondary alcohol was dehydrated with potassium hydrogen sulfate after hydrolysis, 2H5V was... 

The synthesis of 2(2-hydroxy-5-methy lphenyl)2H-4 -vinyl-benzo-triazole was accomplished (31) by a sequence of reactions similar to those which gave 2H5V. The starting material for this synthesis was, however, not o-nitroaniline but 4-ethyl-o-nitroaniline. After diazo-tiation, the diazonium compounds were allowed to react with p-cresol the condensation product gave 2(2-hydroxy-5-methylphenyl)2H-4-ethyl-benzotriazole after reductive cyclization. This compound was acetyl-ated, brominated, dehydrobrominated, and hydrolyzed to 2(2-hydroxy-5-methylphenyl)2H-4 —viny1-benzotriazole. 

Preparation of Ketones. l-[(Trimethylsilyl)methyl]benzo-triazole reacts readily with acyl chlorides to provide the corresponding (benzotriazol-l-yl)methyl ketones in good yields. One example of such reactions is given in eq 1, and similar results are reported for reactions with benzoyl, acetyl, phenylacetyl, and other acyl chlorides. As shown by an example in eq 2, the benzo-triazolyl moiety in (benzotriazol-l-yl)methyl ketones is easily removed by reduction with zinc in acetic acid to provide the corresponding methyl ketones. To prepare higher ketones, lithi-ated l-[(trimethylsilyl)methyl]benzotriazole is alkylated first and then subjected to the regular reactions with acyl chlorides and zinc. Thus, in a reaction of l-[(trimethylsilyl)methyl]benzotriazole with -BuLi followed by benzyl bromide, l-[ l-(trimethylsilyl)-2-phenylethyljbenzotriazole is obtained in 81% yield. Subsequent treatment of this product with 4-methylbenzoyl chloride and then with zinc in acetic acid provides 4-methylphenyl 2-phenylethyl... 

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