A new procedure for synthesis of phosphorylated ynamines

Abstract

Phosphorylated ynamines are commonly formed in reactions of chloroethynylphosphonates with secondary [1] or tertiary amines [2]. In the reactions with secondary amines, the parent amine taken in a double molar excess serves as acceptor of the evolved hydrogen chloride. However, while the reactions with chloroethynylphosphonates with highly basic secondary amines, such as diethylamine (pKa 10.58) [1, 3], morpholine (pKa 8.51), or piperidine (pKa 11.22) [4], in an apolar solvent (anhydrous carbon tetrachloride) proceed vigorously with heat release and afford phosphorylated ynamines in quantitative yields, attempted synthesis of ynamines using secondary amines of moderate or low basicity did not lead to an unequivocal result. In the cited works, the basicities of amines were estimated using the Marvin Sketch program, version 3.5.7 (ChemAxon, http://chemaxon. com/marvin). The pKa values calculated by this program for aromatic amines well fit reference values. We explored the progress of the reaction of dimethyl chloroethynylphosphonate with 1,2,3,4-tetrahydroquinoline (pKa 5.00) in anhydrous CCl4 (reagent molar ratio 1 : 2) by means of H and P NMR spectroscopy and H {P} double resonance (decoupling and INDOR experiments). One hour after reagent mixing, the H {P} INDOR spectrum of the reaction mixture shows two signals: one at P 1.5 ppm (characteristic of phosphorylated ynamines) and the second, stronger signal at P 11 ppm. The H NMR spectrum of the reaction mixture contains a downfield doublet at 5.3 ppm (JHP 11 Hz). This observation together the above phosphorus chemical shift suggests formation of a compound with an sp carbon atom attached to phosphorus and bearing hydrogen. We can thus conclude that the second product is an ynamine hydrochlorinated by the triple bond: