Amines, photochemistry halides

Little is known so far about a-ketoenamines, probably because they are sometimes not directly accessible from the corresponding diketones. Nevertheless, they are useful synthones, especially for heterocyclic synthesis. Compared with /S-ketoen amines, the chemical behaviour of the a-keto-derivatives is somewhat different. They react as enamines, as well as ,)S-unsaturated ketones, which means that they act either as an electrophile or as a nucleophile in the -pvosition. For example, protonation usually occurs at the fi-C atom with subsequent enolization . Aminomethylation according to Mannich takes place in the / -position as welP° . The alkylation with alkyl halide, however, is reported to occur at nitrogen . In addition to electrophilic and nucleophilic chemistry, a-ketoenamines are useful synthons in photochemistry and electrocyclic reactions. 

Likewise, Melchiorre reported that chiral amines 32, so often used in thermal organocatalysis, find use also in photochemistry and form colored EDA complexes with electron-withdrawing substituted benzyl halides (33), and irradiation leads to electron transfer and benzylation of aldehydes (an example in Scheme 8.16 for the synthesis of 34) [25, 26]. 

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