| http://www.w3.org/ns/prov#value | - The starting materials of formula II can be prepared, for example, by reacting a compound of formula ##STR7## or preferably the anhydride or acid chloride thereof, with a corresponding phosphorous acid triester of formula P(OR)3 (IIb) in the presence of a tri-lower alkylamine, for example triethylamine, to form a compound of formula ##STR8## and further reacting the latter with a phosphorous acid
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