A useful magnesium reagent for the preparation of 1,1-difluoro-2-hydroxyphosphonates from diethyl bromodifluoromethylphosphonate via a metal—halogen exchange reaction
Résumé
When (EtO) 2 P(O)CF 2 Br (1) is treated with isopropylmagnesium chloride in THF at low temperature it gives a magnesium species (2) which undergoes reactions with strong electrophiles (HCl, TMSCl, halogens, aldehydes and ketones). The formation of products strongly depends on the reaction conditions. With 1.5 equivalents of (2) between-78°C and 0°C, a conversion of more than 90% of aldehydes and ketones into 2-hydroxyphosphonates (7) and (8) can be achieved. These compounds (7) and (8) in the presence of base (NaH, LDA) are rearranged into 2,2-difluoroethylphosphates without concomitant formation of 1,1-difluoroolefines.
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