Enolates p-dicarbonyl compounds

The best-known reactions belonging to this class are based either on the photo-NOCAS process [32] or on the photochemistry of Barton esters [69]. In the first case, a three-component reaction involving a cyanoarene, an olefin, and a nucleophile (usually the solvent) occurs. The reaction is generally initiated by a PET process between the aromatic and the olefin. The examples presented below are chosen from among the most representative and most recent. A typical reaction is illustrated in Scheme 3.26, where an enolized P-dicarbonyl compound acts as an added nucleophile. 

More complex carbonyl compounds can be much more strongly enolized. P-Dicarbonyl compounds (1,3-dicarbonyl compounds) exist largely in their enol forms, for example (Fig. 19.21). In the enol forms of these compounds, it is possible to form an intramolecular hydrogen bond, thus forcing the equilibrium position away from the diketo forms. There is also conjugation between the carbon—carbon... 

The enolized p-dicarbonyl compounds (318) add photochemically to cyclohexene to yield the cyclobutanols (319). The stereochemistry of the photochemical [2 + 2] adduct of benzene and acrylonitrile has been established. Addition of vinyl acetate to benzene yields only small amounts of the [2 + 2] product The major product is the 1,3-adduct... 

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