Photochemical reaction of α-alkyl-β-oxoamides. Competitive γ- and δ-hydrogen abstraction by excited ketone carbonyl groups
The α-alkyl-β-oxoamides (1a–i) undergo the Norrish Type II photoreaction. The excited ketone carbonyl group in the β-oxoamides (1c, 1f–i) abstracts γ- and δ-hydrogen competitively from the n,π* triplet state. The regioselectivity of the hydrogen abstraction is affected by both the γ- and the δ- substituents. The presence of γ- or δ-substitution increases the γ- or the δ-hydrogen abstraction, respectively. The δ-hydrogen abstraction greatly predominates over the γ-hydrogen abstraction in the photolyses of the α-ethyl-β-oxoamides (1f) and (1i).