Abstract
In this paper, the microwave (MW)-assisted catalyst-free and mostly solvent-free Kabachnik–Fields reaction of amino alcohols, paraformaldehyde, and various >P(O)H reagents (dialkyl phosphites, ethyl phenyl-H-phosphinate, and secondary phosphine oxides) is reported. The synthesis of N-2-hydroxyethyl-α-aminophosphonate derivatives was optimized in respect of the temperature, the reaction time, and the molar ratio of the starting materials. A few by-products were also identified. N,N-Bis(phosphinoylmethyl)amines containing a hydroxyethyl group were also prepared by the double Kabachnik–Fields reaction of ethanolamine with an excess of paraformaldehyde and secondary phosphine oxides. The crystal structure of a 2-hydroxyethyl-α-aminophosphine oxide and a bis(phosphinoylmethyl)ethanolamine was studied by X-ray analysis.
Highlights
Introduction αAminophosphonate derivatives are among the most important organophosphorus compounds [1]
A possible reactive function is the hydroxyl group, which can be alkylated, acylated, or even phosphorylated [6]. Another option is the carboxylic function, which may mean a possibility for further functionalizations [7]. α-Aminophosphonates containing a carboxylic group may be synthesized starting from amino acids [8,9]
Paper, we we introduce introduce the the synthesis synthesis of of 2-hydroxyethyl-α-aminophosphonates
Summary
Kabachnik–Fields reaction reaction of of ethanolamine, ethanolamine, paraformaldehyde, paraformaldehyde, and diethyl. The double Kabachnik–Fields condensation of ethanolamine with an excess of and the diphenylphosphine oxide at 100 ◦ C for 1 h (Table 5, Entry 1) It was found paraformaldehyde and secondary phosphine oxides was studied (Table 5). By using 2.5 equivalents of the diphenylphosphine oxide, the ratio of the mono (8a) and the bis product (12a) remained almost unchanged (Table 5, Entry 4) Further increase in the molar ratios to three equivalents allowed product (12a) remained almost unchanged (Table 5, Entry 4) When both reagents (the a full transformation toward the N,N-bis(diphenylphosphinoylmethyl)ethanolamine (12a), which was paraformaldehyde and the diphenylphosphine oxide) were used in 2.5 equivalents quantity, the obtained in a yield of 95% after purification (Table 5, Entry 6).
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