Journal of the American Chemical Society p. 3940 - 3944 (1990)
Update date:2022-08-17
Topics:
Prathapan, Sreedharan
Loft, Sarah
Agosta, William C.
On either direct irradiation in water or triplet-sensitized irradiation in acetone, pyrimidines 1a-c undergo hydrogen abstraction from an nπ* triplet state, fragmentation, and rearomatization to form 5 (eq 1). Similarly, direct irradiation of quinolines 2a-c in benzene or tert-butyl alcohol furnishes 6 from an nπ* singlet state. Quantum yields for products (Φ5 and Φ6) and Stern-Volmer quenching studies on these reactions (Tables I and II) provide mechanistic information concerning abstraction by aromatic nitrogen. Unlike Φ for abstraction by carbonyl triplets, Φ5 and Φ6 do not increase in hydrogen-bonding solvent, and there is little rate difference in transferring primary, secondary, and tertiary hydrogen in the initial step. Singlet and triplet abstractions show little difference in selectivity, but the singlet reaction is ? 104 faster. Concentration studies show that fragmentation of 1a-c is self-quenched, while reaction of 2a-c is enhanced with increasing concentration.
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