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

The structure of the carbanionic species 4 formed from diethyl(2-oxopropyl)phosphonate and t-BuOK has been studied by 1H, 13C and 31P NMR. In an associating medium (pyridine), a single chelated (C) carbanionic species 4Z (C) is observed. Two slowly interconverting species 4Z and 4E co-exist when the anion-cation interaction is loose, i.e. in Me2SO and when the gegenion K+ is complexed to (2,2,2)cryptand in Me2SO. The anionic carbon of 4Z and 4E is planar, and they have a strong enolate character as shown by the barrier to rotation around the C-1C-2 bond (ΔGc‡∼92 KJ mol−1). Their structures are compared to those of the related E and Z 1-diethylphosphonato-2-trimethylsilyloxypropenes and to (acetylmethylene)triphenylphosphorane.

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