Photolysis of acetophenone derivatives with α‐cyclopropyl substituents

• DOI: 10.1002/poc.3389
• Publication Date: 2014-11-25T07:06:25Z
• Authors: Ranaweera A. A. U...; Geethika K. Weragoda; John Bain; Shinji Watanabe; Manabu Abe; Anna D. Gudmundsd...
• Keywords: 01 natural sciences; 0104 chemical sciences

Laser flash photolysis of cyclopropyl(phenyl)methanone 6 in argon‐saturated methanol yields the triplet ketone (T1K) of 6 that is formed with a rate constant of ~1.7 × 107 s−1(λmax = 360 nm) and has a lifetime of ~1.4 µs. T1Kof 6 decays to form ketyl radical 7 (λmax~300 nm), which dimerizes to form photoproducts, pinacol derivatives 8 and 9. In comparison, photolysis oftrans‐phenyl(2‐phenylcyclopropyl)methanone 1 in argon‐saturated chloroform‐d results incis‐phenyl(2‐phenylcyclopropyl)methanone 2 and a smaller amount of 3, presumably through 1,3‐biradical 11. Nanosecond laser flash photolysis of 1 does not reveal significant transient absorption, although the T1Kof 1 is detected with phosphorescence at 77 K. Density functional theory calculations were used to elucidate the triplet reactivity of 1, 2 and 6 by comparing the feasibility of H atom abstraction, cyclopropyl cleavage and β‐quenching of their triplet ketones. Copyright © 2014 John Wiley & Sons, Ltd.