Norrish/Yang type II reactions

The photochemical reaction that has been most thoroughly investigated from the ionic chiral auxiliary point of view is the well-known Norrish/Yang type II reaction. One example, taken from the work of Patrick, Scheffer, and Scott [36], deals with derivatives of 7-methyl-7-benzoylnorbornane-p-car-boxylic acid (37a, Scheme 8). This compound was treated with a variety of optically pure amines to afford the corresponding 1 1 salts (37b), and in an... 

Chirally modified zeolite Norrish/Yang Type II Reaction Direct excitation Enantiodifferentiation 49-53... 

Pioneering work on the photochemical diastereocontrol in zeolite supercages was reported by Turro and coworkers in 1991 [48]. They investigated the diastereoselective photodecarbonylation of 2,4-diphenyl-3-pentanone (DPP) adsorbed in various cation-exchanged X and Y zeolites to find that the diastereo-selectivity of d9l- over mestf-2,3-diphenylbutane increases in the order LiX NaX < LiY NaY < KY. In 1996, Ramamurthy and coworkers reported the first example of photochemical asymmetric induction in chirally modified zeolites [49], where they employed the Norrish/Yang type II reaction of cis-4-tert-butyl-cyclohexyl aryl ketones to the corresponding cyclobutanols. Since then, a variety of asymmetric photoreactions in zeolite supercages have been reported as reviewed below. 

A. Enantiodifferentiating Norrish/Yang Type II Reactions in Chirally Modified Zeolites... 

For four of the reactions shown in Table 4 (entries 1,5,11, and 12), absolute configuration correlations were established between the reactant and its solid-state photoproduct. Such correlations represent one of the most powerful methods available to the organic chemist for elucidating reaction mechanisms. In the Norrish/Yang type II reaction (entries 1 and 5), for example, it allows an unequivocal determination of which y-hydrogen is abstracted, and for the di-7r-methane rearrangement of dibenzobarrelene derivatives (entries 11 and 12), it tells us precisely which atoms are involved in the formation of the initial cyclopropyldi-carbinyl diradical. 

For a general review on the Norrish/Yang type II reaction, see Wagner, P. and Park, B.-S., Photo-induced hydrogen atom abstraction by carbonyl compounds, in Organic Photochemistry, Vol. 11, Padwa, A., Ed., Marcel Dekker, New York, 1991, chap. 4. 

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