Photofragmentation Norrish type

Scheme 17 Radical cation generation and trapping by Norrish type I photofragmentation...

Levrand, B. and Herrmann, A. (2002) Light induced controlled release of fragrances by Norrish type II photofragmentation of alkyl phenyl ketones. Photochemical e[ Photohiological Sciences, 1, 907-919. 

Rochat, S., Minardi, C., De Saint Laumer, J.-Y., Herrmann, A. Controlled release of perfumery aldehydes and ketones by Norrish type-ll photofragmentation of a-keto esters in undegassed solution. Helv. Chim. Acta 2000, 83, 1645-1671. 

Conversion of Thioketones to Ketones. Thioketones generated by a Norrish-type photofragmentation of a sulfenyl acetophenone are trapped in situ by [3 + 2] dipolar cycloaddition with a silyl nitronate (eq 10). Fluoride treatment of the resulting heterocycle produces the ketone. This transformation is compatible with a variety of functional groups and has been used as part of a synthetic manipulation in which an a-acyl cyclic thioether is converted stereoselectively, with ring enlargement, to a ketolactone (methynolide synthesis). ... 

Poly(o-tolyl vinyl ketone) (5.20) is much more photochemically stable than poly(phenyl vinyl ketone) (5.15). The o-methylbenzoyl group stabilizes the polymer, which would otherwise undergo the Norrish Type II reaction. The effect is due to the photoenolization of this chromophore, a process which competes favourably with the photofragmentation [197, 198] ... 

A few benzoin derivatives decompose by photofragmentation mechanisms other than Norrish Type I. For example, a-halogen acetophenones [28], oxysulfonyl ketones [29], and sulfonyl ketones [30] sufficiently undergo p-cleavage upon UV irradiation and may be used for initiation, a-Dimethylamino-substituted benzoin undergoes both a-cleavage and P-pho-... 

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