Rearrangement Reactions of Cyclic Unsaturated Ketones

Significantly, both cis and trans ring junctures are formed. Cyclohexenone and cyclopentene, for example, give four adducts with about a 2 1 cis.trans ratio. [Pg.1125]

The trans products obviously are more strained. The stereochemistry can be traced to conformational factors in the diradical. For example, the diradical from cyclohexenone and isobutene can be formed in several conformations. [Pg.1126]

In hydrocarbon solvents, the principal products from cyclopentenones result from hydrogen abstraction processes. Irradiation of cyclopentenone in cyclohexane gives a mixture of 2- and 3-cyclohexylcyclopentanone. These products can be formed by intermolecular hydrogen abstraction, followed by recombination of the resulting radicals. It is interesting that as in the alkene cycloaddition reaction, reactivity is observed at both C(2) and C(3) of the excited enone system. [Pg.1126]

If a substituent chain is present on the cyclopentenone ring, an intramolecular hydrogen abstraction can take place. [Pg.1126]

The bicyclic product is formed by coupling of the two radical sites, whereas the unsaturated side chain results from an intramolecular hydrogen atom transfer. These reactions can be sensitized by aromatic ketones and quenched by typical triplet quenchers, and are therefore believed to proceed via triplet excited states. [Pg.1126]

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