Scheme 10:

Isomerization of dimethyl maleate (19b) to fumerate 23 and the respective carbon–phosphorus ylide 21a. SpectrumA: section of the 1H NMR spectra of dimethyl maleate (19b). Spectrum B: section of the 1H NMR of a 1:1 mixture of nBu3P/dimethyl maleate (1:1) in toluene-d8 at 296 K after a reaction time of ≤15 min.

© De Gruyter