Structural studies of carbanionic species α to a phosphoryl group; anion from ketophosphonate comparison with related enoxysilanes and p‐ylid

Abstract

Abstract The structure of the carbanionic species 4 formed from diethyl(2‐oxopropyl)phosphonate and t ‐BuOK has been studied by 1 H, 13 C and 31 P NMR. In an associating medium (pyridine), a single chelated (C) carbanionic species 4 Z (C) is observed. Two slowly interconverting species 4 Z and 4 E co‐exist when the anion‐cation interaction is loose, i.e. in Me 2 SO and when the gegenion K + is complexed to (2,2,2)cryptand in Me 2 SO. The anionic carbon of 4 Z and 4 E is planar, and they have a strong enolate character as shown by the barrier to rotation around the C‐1C‐2 bond (Δ G c ‡∼92 KJ mol −1 ). Their structures are compared to those of the related E and Z 1‐diethylphosphonato‐2‐trimethylsilyloxypropenes and to (acetylmethylene)triphenylphosphorane.