THE SOLUTION STRUCTURE OF BETA,GAMMA-DIOXOALKYL(TRIPHENYL)PHOSPHONIUMSALTS

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 so lution mainly as the E and Z enol structures b and c. The salt 6 exist s as a mixture of the keto form a and one enol form assumed to be b. S imilarly the bis(phosphonium salt) 16 exists entirely with one end in the keto form and the other in the enol form. The ylide/phosphonium sa lt 17 obtained from 16 by treatment with base also exists as an enol w hich is resistant to further deprotonation. Fully assigned C-13 NMR sp ectra are presented for all the structures involved. (C) 1998 Elsevier Science Ltd. All rights reserved.