Highly stereospecific generation of helical chirality by vicinal diamine: Determination of enantiomeric purity.

摘要

A convenient and general chiral derivatization protocol for determining the enantiopurity and absolute chirality of chiral vicinal diamine by 1H NMR spectroscopic analysis is studied. The method involves covalent derivatization of one equivalent dimaine with two equivalents of chiral derivatization agent. The afforded diastereoisomeric diimines give rise to well-resolved diastereotopic resonances in their 1H NMR spectra, enabling accurate determination of enantiomeric purity of diamine in interest. Molecule mechanics, DFT computations, and X-ray crystallography all confirm the 1H NMR experimental result, which allows the absolute configuration assignment of diamine.;The generation of helical chirality by translating chirality from vicinal diamine to achiral receptor is investigated. The unprecedented stereoselectivity is controlled by two hydrogen bonds. We discovered that one of the H-bond is a charge species, generated due to the electron withdrawing property of the receptor. The strong charge interaction is responsible for creating the helical chirality. Excellent agreement between DFT computation, crystallography and excitor chirality CD spectra allows explicit assignment of the absolute configuration of the diamine.