Preparation of fluorohalomethylmagnesium halides using highly active magnesium metal and their reactions

Highly active magnesium (Rieke magnesium) reacts with fluorohalomethanes at −100 °C forming the corresponding fluorohalomethylmagnesium halides, which undergo nucleophilic substitution with silyl halides or nucleophilic addition with aldehydes or ketones. Whereas the stability of dibromofluoromethylmagnesium bromide (2a) was sufficient to provide acceptable product yields with dimethylphenylsilyl chloride, benzaldehyde, butyraldehyde or acetophenone as electrophiles, other fluoroorganomagnesium halides, bromodifluoromethylmagnesium bromide (2b), bromochlorofluoromethylmagnesium bromide (2c) and trifluoromethylmagnesium iodide (2d) displayed only very limited stability and thus the corresponding yields of reactions with electrophiles were low.