ISSN:
1434-193X
Keywords:
Cyclopropanation
;
Chromium
;
Catalysis
;
Carbene complex
;
Diazo compounds
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The [2 + 1] cycloaddition reaction of electron-rich alkenes such as enol ethers with 9-diazo-9H-fluorene (1) is efficiently catalyzed by pentacarbonyl(η2-cis-cyclooctene)chromium(0) (2). This cyclopropanation reaction shows a pronounced preference for electron-rich C=C bonds, as demonstrated by the regioselective reactions of allyl vinyl ether and 2-vinyloxyethyl acrylate; the [2 + 1] cycloaddition proceeds via the carbene complex intermediate 13, which has been detected by 13C-NMR spectroscopy in the course of the reaction. (Z)-Propenyl benzyl ether yields spirocyclopropane 21 with retention of the configuration of the former olefinic double bond. Whereas diazo compounds 22 and 23 react with ethyl vinyl ether to give low yields of cyclopropanes, the dibenzocycloheptenylidene and diarylcarbene precursors 24 and 25 afford moderate yields of olefin metathesis products 29-31. The competition between cyclopropanation and olefin metathesis reflects the propensity of the carbene complex intermediates to undergo decarbonylation.
Type of Medium:
Electronic Resource
Permalink
