Synthesis of Stable Carbamate Phosphorus Ylides by a Four-Component Reaction And Dynamic ¹H-Nmr Study of the Energy Barriers for the Rotation around the Carbon–Nitrogen Single Bond and the Carbon–Carbon Double Bond

GRAPHICAL ABSTRACT

Abstract

A stable phosphorus ylide is obtained in high yield by a four-component reaction between triphenylphosphine and dimethyl acetylendicarboxylate in the presence of the intermediate product formed from phenyl isocyanate and substituted phenols in dichloromethane at room temperature. This stable phosphorus ylide exists in solution as a mixture of two geometrical isomers resulting from restricted rotation around the carbon–carbon partial double bond due to the conjugation of ylide moiety with an adjacent carbonyl group. Dynamic effects are observed in ¹H-NMR spectra that are attributed to restricted rotation around the carbon–carbon double bond and the carbon–nitrogen single bond. These effects are used to calculate the free activation energy (ΔG^‡) and other activation parameters, such as ΔH^‡, ΔS^‡, and E_a.

Keywords:

• Dynamic ¹H-NMR
• free activation energy
• phosphorus ylide
• rotational energy barrier