Norrish type ketone photoelimination

The groups of Pete and Rau also employed chiral amino alcohols for the enantioselective protonation of simple enols 23a-c that were photochemically generated from 2-/-butyl indanones and tetralones 22a-c by a Norrish type II photoelimination (Scheme 9) [41,42]. Best enantioselectivities were obtained at — 40°C in acetonitrile with 0.1 equivalent of the chiral amino alcohol. In the case of indanone 22a, the selectivity reached 49% ee with (— )-ephedrine ent-18) and could not be further enhanced by the camphor derived inductor 20. With this amino alcohol, enantioselectivities over 80% ee were induced in the case of tetralone 22b. A benzyl substituent in place of the methyl group led to substantial decrease of the selectivity to 47% ee. Linear ketones gave low yields and enantioselectivities around 9% ee. 

P. J. Wagner, P. Kian, Chapter 52 Norrish Type II Photoelimination of Ketones Cleavage of 1,4-Biradicals Formed by y-Hydrogcn Abstraction, in CRC Handbook of Organic Photochemistry and Photobiology, W. M. Horspool, F. Lengi, (Eds.), CRC Press, Boca Raton, 2003, p. 1-31. 

UV and y-radiation of poly(methyl isopropenyl ketone) produced random chain scission at 23 °C. The presence of air increases unexpectedly the main chain scission of the polymer under y-radiation [377]. In a series of publications [378] the radiolysis and photolysis of poly(phenyl vinyl ketone), poly(vinyl benzophenone), and poly(/-butyl vinyl ketone) [357] were described. The authors stated that photodegradation of poly (phenyl vinyl ketone) occurred by the abstraction of a hydrogen in the y-position to a carbonyl group, followed by chain scission by a Norrish type II photoelimination mechanism. 

A novel example of the cleavage of an imine to a nitrile has been reported.142 Irradiation of i T-(l-phenyl-2-propylidene)benzylamine (223) affords acetonitrile, toluene, and bibenzyl, by a process which is at least formally analogous to the Norrish type I cleavage of ketones. On irradiation, the amine (224) is converted into the quinoline (225) by an unprecedented photoelimination of water.143... 

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