| Abstract
| - Cyclopentadienylidenetriphenylphosphorane (the Ramirez ylide), unexpectedly and contrary to a numberof earlier reports, has been shown to be like pyrrole in undergoing electrophilic substitution on thecyclopentadienide ring at either the 3- or the 2-position, depending on the electrophile. Formylationunder Vilsmeier conditions and addition of tetracyanoethylene occurs at the 3-position, while activatedacetylenes and the nitrosyl electrophile substitute at the 2 position. The 3-formylated product was reducedto the 3-methyl derivative and it also reacted under Knoevenagel conditions to give a number of novelcondensation products. The results of single-crystal X-ray crystallographic analyses are given for four ofthe compounds studied, and a careful 2D NMR analysis of all of the compounds was performed in orderto develop a reliable method for the unambiguous assignment of the regiochemistry of adduct formation.
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