Cyclopentadienones in the reaction of alkynes with cyclopropylcarbene-chromium complexes

✍ Scribed by James W. Herndon; Seniz U. Tumer

• Publisher: Elsevier Science
• Year: 1989
• Tongue: French
• Weight: 149 KB
• Volume: 30
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)95183-9

✦ Synopsis

Reaction of alkynes having bulky substituents with pentacarbonyl[cyclopropyl(methoxy)methylene]chromium(0) (1) provided cyclopentadienone derivatives. Cyclopentadienones were easily hydrogenated to the corresponding cyclopentenones using chromium hexacarbonyl and water, with no problems resutting from overreduction to the cyclopentanone.

Recently, we reported that cyclopropylcarbene-chromium complexes react with alkynes to generate cyclopentenone derivatives (Scheme 1)1.

We proposed two mechanistic schemes for the reaction, both involving reduction of cycbpentadienones as the penultimate step in the reaction. Water was required in the reaction as the source of H1 and H2, presumably while chromium(O) is oxidized to chromium(lll). Cycbpentadienones are typically highly reactive and unstable2, and could not be isolated from the reaction. Herein we report our attempts to isolate cycbpentadienones from the reaction, and their subsequent reduction to cyclopentenones.