Phenylene-Bis-Aminomethanephosphonic and Phosphonous Acids

Synthesis of 1,4-phenylene-bis-aminomethanephosphonates: The stereochemical aspect

“…Our observation concerning the stereochemistry of addition of phosphites to the azomethine bond of bis-imines was similar to Barycki's [11] observation; we determined the formation of the exclusive diastereoisomer. It was confirmed, by the analysis of the post-reaction mixture, that no other product part from unreacted substrates was formed.…”

“…Barycki et al [11] performed this reaction without solvent, but this method turned out to be ineffective, as the separation and purification of the products were rather troublesome. The authors did not isolate the esters but hydrolyzed the products to the acids.…”

“…Products were obtained in 46-58% yield, which is satisfactory and relatively high, considering that the addition of phosphite to bis-Schiff bases is much more difficult than the mono-addition [11]. All results are collected in Table 1.…”

“…Finally Zimmer and Thomas [15] synthesized 1,4-phenylene-bis-(N-p-nitroanilinomethane)-bis-phosphonates, which were subsequently utilized in further reactions. Barycki et al [11] have observed an intriguing phenomenon. They noticed that the final diacid gave one set of signals in the 1 H NMR spectrum and a single signal in the 31 P NMR spectrum, concluding that the attack on the second azomethine bond is stereocontrolled; thus the reaction is stereoselective.…”

“…But they neglected completely the spectral characterization of products. Issleib et al [10] Barycki et al [11] and Garncarz [12] reported the hydrolysis of tetraethyl 1,4-phenylenebis-(N-benzyl-aminomethane)-bis-phosphonate and tetraethyl 1,4-phenylene-bis-(N-benzhydrylaminomethane)-bis-phosphonate as a key step in the synthesis of the corresponding acids. The synthesis of the esters was carried out without any solvent, and they neither isolated nor characterized these esters.…”