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Updated: Aug 18, 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
An efficient three-step synthesis of cyclopenta[b]pyrans via 2-donor-substituted fischer ethenylcarbenechromium
Armin de Meijere1, Heiko Schirmer, Frank Stein
1Institut für Organische und Biomolekulare Chemie der Georg-August-Universität Göttingen, Germany.
Abstract:
A wide range of cyclopenta[b]pyrans 4 has been synthesized in a one-pot reaction by treatment of different 2-donorsubstituted ethenylcarbenechromium complexes 2 with alkynes in THF in moderate to excellent yields (41-90 % for 14 out of 25 examples). The starting materials 2 are readily available in good to excellent yields (76-99 % for 25 out of 36 examples) by Michael addition of amines, alcohols and thiols, respectively, to the corresponding alkynylcarbenechromium complexes 1. Due to their 10 pi-electrons in a cross-conjugated bicyclic system, cyclopenta[b]pyrans have been termed pseudoazulenes, as they indeed have similar UV/Vis-spectroscopic properties.
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