Synthesis, spectroscopic characterization and crystal structure of a new chiral amidophosphoester

The chiral amidophosphoester families have found widespread use in the preparation of different classes of drugs, and for processing of biologically active compounds [1]. We report here the synthesis of single-enantiomer amidophosphoester (C6H5O)2P(O)[(R)-(+)-NHCH(CH3)(C6H4-4-CH3)] (I) and its characterization by IR, NMR, mass, optical rotation and single crystal X-ray diffraction. The compound crystallizes in monoclinic system with chiral space group P21. The asymmetric unit is composed of two independent molecules. The P atoms have a distorted tetrahedral (O)2P(O)(N) configuration. In the crystal, chiral one-dimensional hydrogen-bonded architecture, formed along b axis, is mediated by classical N—H…O(P) and weak C—H…O(P) hydrogen bonds. This architecture includes ?11(2), ?22(10), ?22(8) and ?21(8) graph-set motifs. In the IR spectrum, the band centered at 3174 cm–1 is attributed to the NH stretching frequency. The melting point of title structure (393 K) is a few lower than the closely related analogous compound (C6H5O)2P(O)[(R)-(+)NHCH(CH3)(C6H5)]2 (408 K) [2]. The phosphorus signal appears at –0.07 ppm, in comparison with the signal at –0.81 ppm for this analogous compound noted [2]. The two diastereotopic phenyl groups reveal two sets of signals in 1H- and 13C{1H}-NMR spectra. The specific optical rotation is measured as [?]?20 = 51° (c 0.009, MeOH).