Coupling of Cyclopropylcarbene-Chromium Complex With Ferrocenyl Alkynes: Synthesis of 5-Ferrocenyl and 4-Ferrocenyl

Abstract

The coupling of ferrocenyl alkynes with cyclopropylcarbene-chromium complex leads to ferrocenyl-substituted 2-cyclopentenones with or without a hydroxy substituent, namely 4-cyclopentene-1,3-diones, 2-cyclobutenones, and α,β-unsaturated aldehydes in varying amounts. The reaction initially produces a cyclopentadienone intermediate, then to the double bond of which, bearing a ferrocenyl group, addition of water occurs to afford hydroxy-substituted 2-cyclopentenones. In all the products, the hydroxy group ends up α to the ferrocenyl moiety. In contrast, where no addition of water occurs, the alkenic bond is reduced to give 2-cyclopentenones. A secondary reaction product, namely 4-cyclopentene-1,3-dione, is formed by hydrolysis of the cyclopentadienone intermediates. © 2007 Elsevier Ltd. All rights reserved.