Dioxaphosphorinane chair to half-chair conversion caused by cis- to trans-enol transformation of the β-ketoester substituent

Abstract

The X-ray single crystal structure 5,5-dimethyl-2-(methoxycarbonyl-3′-oxo-2′-butyl)-2-oxo-1,3,2-dioxaphosphorinane (I) reveals an unusual half-chair conformation of the dioxaphosphorinane substituent on a trans-enol ring. NMR and IR solution data provide support that the same structure displays a strong conformational preference while the minor forms are chair conformers with an axial and equatorial cis-enol ring. © 1995.