title: A re-evaluation of the electrophilic substitution reactions of the Ramirez ylide.
abstract: 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.
authors.affiliation: 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
authors.forename: Lee J
authors.initials: LJ
authors.lastname: Higham
authors.forename: Jimmy
authors.initials: J
authors.lastname: Muldoon
authors.forename: P Gabriel
authors.initials: PG
authors.lastname: Kelly
authors.forename: David M
authors.initials: DM
authors.lastname: Corr
authors.forename: Helge
authors.initials: H
authors.lastname: Müller-Bunz
authors.forename: Declan G
authors.initials: DG
authors.lastname: Gilheany
mesh_terms: D018360:Crystallography, X-Ray; D003517:Cyclopentanes / Q000737:chemistry*; D004583:Electrons; D008958:Models, Molecular; D015394:Molecular Structure; D010753:Phosphoranes / Q000737:chemistry*
chemical_list: D003517:Cyclopentanes; D010753:Phosphoranes; C525415:cyclopentadienylidenetriphenylphosphorane