The solution structure of β,γ-dioxoalkyl(triphenyl)phosphonium salts

The simple phosphonium salts 4 and 5 have been fully characterised for the first time and are found by NMR spectroscopy to exist in CDCl3 solution mainly as the E and Z enol structures b and c. The salt 6 exists as a mixture of the keto form a and one enol form assumed to be b. Similarly the bis(phosphonium salt) 16 exists entirely with one end in the keto form and the other in the enol form. The ylide/phosphonium salt 17 obtained from 16 by treatment with base also exists as an enol which is resistant to further deprotonation. Fully assigned C-13 NMR spectra are presented for all the structures involved. (C) 1998 Elsevier Science Ltd. All rights reserved.