Cesium fluorosulfate

All four A-halobenzotriazoles are known. 1-Fluorobenzotriazole 35 was obtained by treating benzotriazole with excess cesium fluorosulfate (91T7447) (Scheme 13). 

Indirect fluorination has been carried out using metallo-indoles. Hodgson et al used ipso substitution of 2- and 3-(trimethylstannyl)-l-(p-toluenesulfonyl)indoles. Of several fluorinating agents tried, cesium fluorosulfate was the best [43]. 5-Methoxyindoles lithiated in the 4-position were fluorinated by Wfluorobenzene-sulfonimide to prepare 4-fluoro analogs of serotonin and melatonin [44]. 

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