A Re-Evaluation of the Electrophilic Substitution Reactions of the Ramirez Ylide
作者:Lee J. Higham、Jimmy Muldoon、P. Gabriel Kelly、David M. Corr、Helge Müller-Bunz、Declan G. Gilheany
DOI:10.1021/jo7014104
日期:2007.11.1
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
{(<i>E</i>)- and {(<i>Z</i>)-2-[α,β-bis(methoxycarbonyl)vinyl]cyclopentadien-1-ylidene}triphenylphosphorane
作者:Lee J. Higham、P. Gabriel Kelly、Helge Müller-Bunz、Declan G. Gilheany
DOI:10.1107/s0108270104006067
日期:2004.5.15
The Ramirez ylide undergoes electrophilic substitution with dialkyl acetylenedicarboxylates, yielding a mixture of the Z and E adducts. The crystal structure analyses of the two adducts formed using dimethylacetylene, viz. dimethyl ( E)and (Z)-1-[2-(triphenylphosphoranylidene) cyclopentadien-1-yl] ethylenedicarboxylate, both C29H25O4P, explain an unusual chemical shift observed for the vinyl H atom of the Z adduct, which had previously precluded a definitive assignment of the isomers. In addition, the structures explain why only one of the isomers reacts further with acetylene esters to produce azulenes with a rare substitution pattern.