A useful magnesium reagent for the preparation of 1,1-difluoro-2-hydroxyphosphonates from diethyl bromodifluoromethylphosphonate via a metal—halogen exchange reaction

Abstract

When (EtO) 2P(O)CF 2Br ( 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 depends strongly on the reaction conditions. With 1.5 equivalents of 2 between −78 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.