Stacked Naphthyls and Weak Hydrogen-Bond Interactions Govern the Conformational Behavior of <i>P</i>‑Resolved Cyclic Phosphonamides: A Combined Experimental and Computational Study

Abstract

<i>P</i>-Enantiomerically pure cyclic phosphonamides have been synthesized via a cyclization reaction of (<i>S</i>,<i>S</i>)-aminobenzylnaphthols with chloromethylphosphonic dichloride. The reaction is highly stereoselective and gives almost exclusively (<i>S</i>,<i>S</i>,<i>S</i>_P)-cyclic phosphonamides in good yields. Analysis of the X-ray crystal structures shows clearly that the cyclization reaction forces the two naphthyl rings into a stable parallel displaced stacking assembly and indicates also the existence of intramolecular CH···π interactions and weak forms of intermolecular hydrogen bondings, involving the oxygen and the chlorine atoms. QM computations and NMR spectra in solution confirm the stacked molecular assembly as the preferred arrangement of the two naphthyl groups