A re-evaluation of the electrophilic substitution reactions of the Ramirez ylide.
Cyclopentadienylidenetriphenylphosphorane (the Ramirez ylide), unexpectedly and contrary to a number of earlier reports, has been shown to be like pyrrole in undergoing electrophilic substitution on the cyclopentadienide ring at either the 3- or the 2-position, depending on the electrophile. Formylation under Vilsmeier conditions and addition of tetracyanoethylene occurs at the 3-position, while activated acetylenes and the nitrosyl electrophile substitute at the 2 position. The 3-formylated product was reduced to the 3-methyl derivative and it also reacted under Knoevenagel conditions to give a number of novel condensation products. The results of single-crystal X-ray crystallographic analyses are given for four of the compounds studied, and a careful 2D NMR analysis of all of the compounds was performed in order to develop a reliable method for the unambiguous assignment of the regiochemistry of adduct formation.
Higham
Lee J
LJ
School of Chemistry and Chemical Biology, Centre for Synthesis and Chemical Biology, Conway Institute for Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland. lee.higham@ncl.ac.uk
Muldoon
Jimmy
J
Kelly
P Gabriel
PG
Corr
David M
DM
Müller-Bunz
Helge
H
Gilheany
Declan G
DG
D018360:Crystallography, X-Ray; D003517:Cyclopentanes / Q000737:chemistry*; D004583:Electrons; D008958:Models, Molecular; D015394:Molecular Structure; D010753:Phosphoranes / Q000737:chemistry*
D003517:Cyclopentanes; D010753:Phosphoranes; C525415:cyclopentadienylidenetriphenylphosphorane