Synthesis and reactions of 2,2,2‐trihaloethyl α‐hydroxyiminobenzylphosphonates. The influence of the ester group on the chemistry of phosphonates

AbstractArbuzov reactions of diethyl 2,2,2‐trihaloethyl phosphites (3) with benzoyl chloride afforded ethyl 2,2,2‐trihaloethyl benzoylphosphonates (4). The reactions of 4 with NH2OH.HCl led to the formation of methyl benzoate and ethyl methyl H‐phosphonate as a result of alcoholysis of 4, followed by alkoxy group exchange. Methanol solutions of benzoylphosphonates 4 were found by 31P NMR spectroscopy to contain considerable proportions of hemiacetals, 7, which undergo base‐catalyzed CP bond cleavage. The formation of hemiacetals from benzoylphosphonates 4 is suppressed in 2‐propanol, and in this solvent the corresponding oximes 2 could be obtained in good yields. Reactions of methyl benzoylphosphonochloridate (10) with 2,2,2‐trihaloethanols, in CH2Cl2, gave methyl 2,2,2‐trihaloethyl benzoylphosphonates (11) which could be converted directly to oximes 12 by NH2OH.HCl in a one‐pot procedure. In contrast to the previously studied dimethyl (E)‐α‐hydroxyiminobenzylphosphonate, which underwent thermal Beckmann rearrangement to afford N‐benzoylphosphoramidates, both (E) and (Z)‐trihaloethyl esters 2 and 12 underwent fragmentation to benzonitrile and to the corresponding dialkyl hydrogen