(E)-(Hydroxyimino)(hydroxymethoxyphosphinyl)acetic Acid: Synthesis and pH-Dependent Fragmentation

Article abstract of DOI:10.1016/0040-4039(95)02099-3

In contrast to both its parent "troika" acid (E-1, a phosphorylating agent at pH 7 and 25 deg C) and its C-methyl isomer (E-2, which is stable at both acidic and neutral pH), (E)-(hydroxyimino)(hydroxymethoxyphosphinyl)acetic acid E-3 was unreactive at pH 7 and 25 deg C but at pH 1.5 fragmented to methyl phosphate 10 (15percent) and methyl phosphorocyanidate 11 (85percent).The minor product is consistent with solvent phosphorylation, the reaction exclusively observed with E-1.The non-phosphorylating fragmentation pathway is proposed to involve a preliminary E -> Z isomerization of 3 prior to C_α-C_β cleavage.Dual fragmentation pathways were also detected (31P NMR) when the DCHA⁺ salt of E-3 (E-9) was heated in acetonitrile or EtOH; in addition to phosphorylation products (16-19percent), 11 was formed (81-84percent).Reaction of E-9 in refluxing EtOH:t-BuOH (1:1) showed low stereoselectivity in product formation (ca. 3:1 ethyl methyl phosphate : t-butyl methyl phosphate), supporting a dissociative phosphorylation process.