Abstract
In search of novel pentalenide ligands for use in organometallic chemistry and homogeneous catalysis, we report the scope of a straightforward base-promoted Michael annulation of cyclopentadienes with α,β-unsaturated ketones that allows the introduction of symmetrical as well as unsymmetrical aryl and alkyl substitution patterns including electron-donating as well as electron-withdrawing substituents. More than 16 examples of various isomers of 1,3,4,6-tetraarylated dihydropentalenes have been synthesized in isolated yields of up to 78%, representing a substantial expansion of the range of dihydropentalene scaffolds known to date. Double bond isomerization between the two pentacyclic rings in 1,2-dihydropentalenes with electronically different substituents occurred depending on the polarization of the molecule. The melting points of the air-stable dihydropentalenes decrease, and their solubilities in organic solvents improve with increasing substitution and decreasing symmetry of the molecule. A competitive pseudo-retro-aldol pathway produces 1,3,6-triarylated monocyclic pentafulvenes as side products in yields of 9-68%, which can be cleanly isolated (8 new examples) and used for other synthetic purposes, including separate cyclization to other dihydropentalenes.
Original language | English |
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Pages (from-to) | 13790-13802 |
Number of pages | 13 |
Journal | Journal of Organic Chemistry |
Volume | 87 |
Issue number | 21 |
Early online date | 5 Oct 2022 |
DOIs | |
Publication status | Published - 4 Nov 2022 |
Funding
We thank the Royal Society (awards UF160458 and EA180091) and the University of Bath for funding this work. We also thank Tim Woodman and John Lowe (University of Bath) for advice and support with NMR spectroscopy and Shaun Reeksting (University of Bath) for help with mass spectrometry. Hugh J. Sanderson and Jonathan Schütte are acknowledged for providing samples of 1,4-di- p-tolylcyclopentadi-1,3-ene and ( E)-2,2,6,6-tetramethylhept-4-en-3-one.
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Electrospray Time-of-Flight Mass Spectrometer (Open-Access)
Material and Chemical Characterisation (MC2)Facility/equipment: Equipment