Connect Four: Tetraarylated Dihydropentalenes and Triarylated Monocyclic Pentafulvenes from Cyclopentadienes and Enones

Niko A Jenek, Marek Balschun, Stuart M Boyt, Ulrich Hintermair

Research output: Contribution to journalArticlepeer-review

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 languageEnglish
JournalJournal of Organic Chemistry
Early online date5 Oct 2022
DOIs
Publication statusE-pub ahead of print - 5 Oct 2022

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