A-Pyrone complexes

Pyroglycolytic pathway, production, 38 383 Pyrolysis reactions, in synthesis of carbonyl clusters, 30 141-143 a-Pyrone complexes with cobalt, 12 283 with iron, 12 275... 

Whereas Fischer-type chromium carbenes react with alkenes, dienes, and alkynes to afford cyclopropanes, vinylcyclopropanes, and aromatic compounds, the iron Fischer-type carbene (47, e.g. R = Ph) reacts with alkenes and dienes to afford primarily coupled products (58) and (59) (Scheme 21). The mechanism proposed involves a [2 -E 2] cycloaddition of the alkene the carbene to form a metallacyclobutane seeMetallacycld) (60). This intermediate undergoes jS-hydride elimination followed by reductive elimination to generate the coupled products. Carbenes (47) also react with alkynes under CO pressure (ca. 3.7 atm) to afford G-ethoxy-a-pyrone complexes (61). The unstable metallacyclobutene (62) is produced by the reaction of (47) with 2-butyne in the absence of CO. Complex (62) decomposes to the pyrone complex (61). It has been suggested that the intermediate (62) is transformed into the vinylketene complex... 

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