Syntheses of 4‐(2‐hydroperoxy‐2,2‐diarylethyl)‐3,5‐dimethylpyrazoles, 4‐(2‐hydroxy‐2,2‐diarylethyl)‐3,5‐dimethylpyrazoles and the related compounds

The reactions of 1,1‐disubstituted ethenes with 2,4‐pentanedione in the presence of manganese(III) acetate and atmospheric oxygen yielded 4‐acetyl‐6,6‐diaryl‐3‐methyl‐1,2‐dioxan‐3‐ols. The latter gave 4‐(2‐hydroperoxy‐2,2‐diarylemyl)‐3,5‐dimethylpyrazoles by the reaction with hydrazines in methanol‐acetic acid (1:1 v/v) at 50° in 15‐77% yields, or 4‐(2‐hydroxy‐2,2‐diarylethyl)‐3,5‐dimethylpyrazoles by the reaction with hydrazines in methanol in 2‐78% yields. The acid‐catalyzed reaction of 4‐(2‐hydroperoxy‐2,2‐diarylethyl)‐3,5‐dimethylpyrazoles yielded 4‐(aroylmethyl)‐3,5‐dimethylpyrazoles (15‐55%) and 4‐(2,2‐diarylethenyl)‐3,5‐dimethylpyrazoles (9‐29%).