Cyclopentadienone epoxides

This includes two new pathways in cyclohexa-2,4-dienone 4,5-epoxides, the first involving the photorearrangement of the 6,6-dimethyl derivative (115) to the enol lactone (116) via the cyclopropane(117), and the second providing the first example of a-cleavage in systems of this type. Carbon-oxygen bond homolysis is almost certainly implicated in the photorearrangement of cyclopentadienone epoxide.98... 

Sufficient evidence has now been obtained to provide an explanation for the photorearrangement of pyran-4-ones to the isomeric pyran-2-ones.217 An oxabicyclohexenyl zwitterion and a cyclopentadienone epoxide have been established as intermediates in this rearrangement, and the process is illustrated for 3,5-dimethylpyran-4-one (270) in Scheme 21. Related transformations have been observed in 3-hydroxypyran-4-ones218 and in the... 

A facile synthesis of cyclopentadienone epoxides via thermal rDA cycloreversion of a tricyclodece-none epoxide and its acetal derivatives has been applied to the preparation of cyclopentanoid antibiotics. - This procedure has been used in an efficient synthesis of terrein, a mould metabolite from Aspergillus terreus, by rDA synthesis of cyclopentadiene epoxide intermediate (57). FVP conditions for these reactions typically involve temperatures of 420-600 C. Furan-derived DA adducts have also been used to generate cyclopentadienone epoxides. The thermal rDA reaction of the furan-derived DA adduct (58) proceeds at temperatures as low as 330 °C with complete cycloreversion and generation of epoxide (59) in nearly quantitative yield (equation 32). Subsequent elaboration led to epipentenomycin derivatives such as (60). 

Careful re-investigation of the photolysis products of 3,5-dimethyl-y-pyrone in trifluoroethanol (reported last year ") by preparative t.l.c. (Si02) has revealed the presence of two minor, but mechanistically significant, products. One, identified as l,3-dimethyl-6-oxabicyclo[3.1.0]pent-3-en-2-one (145), is the first isolable example of the hitherto elusive cyclopentadienone epoxides, whidi have long been postulated as intermediates in these photolyses. This dienone epoxide is the photo-precursor of the final product, i.e. the isomeric 3,6-dimethyl-a-pyrone, but not of the trifluoroethanol adduct (146). This latter product, as suggested previously, derives directly from the zwitterionic precursor of the bicyclopent-3-en-2-one (145). The other product proved to be cyclopent-l-ene-3,5-dione (147), a photo-rearrangement product of (145). 

Cyclooctadiene-1,5, 23, 62, 445 Cyclooctane-1,2-diol, 384 Cyclooctane-1,5-diol, 64 Cyclooctanol, 183 Cyclooctatetraene, 23 Cyclooctatetraene epoxide, 306, 519 Cyclooctatetraeneiron tricarbonyl, 567 Cyclooctene, 23, 183, 445 Cyclooctene oxide, 334 Cyclooctyl fluoride, 183 Cyclopentadiene, 123, 291 Cyclopentadienone, 454 iT-CycIopentadienylcobalt dicarbonyl, 153-154... 

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