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Updated: Aug 24, 2026

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
[(E)- and [(Z)-2-[alpha,beta-bis(methoxycarbonyl)vinyl]cyclopentadien-1-ylidene]triphenylphosphorane
Lee J Higham1, P Gabriel Kelly, Helge Müller-Bunz
1Department of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland.
Abstract:
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 C(29)H(25)O(4)P, 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.
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