Nitroxides, photoreactions

The spin label in question may as well be in the carboxylic acid fragment as in the alcohol moiety. Photoreactive esters bear azido groups in their carboxylic acid moieties. The esterification of nitroxide- or azide-bearing carboxylic acids with complex alcohols and CDI is illustrated in Table 3-6 by way of some examples. 

Decomposition of azo compounds and peroxides provides the alkoxyamine by the nitroxide-trapping of the primary radicals [29]. The radicals produced by hydrogen abstraction with oxy radicals are also trapped by the nitroxide [242, 243]. In the photoreaction, alkoxyamines were isolated with high yields [244]. The reactions of Grignard reagents with nitroxides [215] and the coupling reaction of sodium nitroxides with bromo compounds [234,235] are also used. The hydrolysis of 56 followed by the reaction with acyl or alkyl halides afforded alkoxyamines with various functional groups,63 (Eq. 68) [245-251] ... 

Veciana, J., Cirujeda, J., Rovira, C., Molins, E. andNovoa, J. J. (1996). Organic ferro-magnets. Hydrogen bonded supramolecular magnetic organizations derived from hydroxylated phenyl a-nitronyl nitroxide radicals. J. Phys. I Ft, 6, 1967-86. [201] Venkatesan, K. and Ramamurthy, V. (1991). Bimolecular photoreactions in crystals. In Photochemistry in organized and constrained media (ed. V. Ramamurthy), pp. 133-84. VCH Publishers, Weinheim. [236]... 

The dimer of (74) is isolated as one of the products. In the flow ESR spectra, nitroxides (76) and (77) can be recognized. These are proposed to arise by H-abstraction from (74) by a cyclobutoxy radical, giving (75), which either reacts with a further molecule of (74), yielding (76), or undergoes, 5-exo ring closure to (77). The steroidal nitrite (78) (Scheme 17) yields 50% of the ketone (79) and 16% of the alcohol (80) when photolysed in the solid state (X > 300 nm), but only 5% of (79) and 52% of the Barton-type product (81) when photolysed in toluene solution. It is usual for ketones to be produced only in low yields from photoreactions of nitrites in solution, and so the promotion of this reaction pathway in solid-state photolysis is of considerable interest. Similar results were obtained for the solid-state photolyses of a number of other steroidal nitrites, but nitrites prepared from acyclic alcohols showed much less selectivity in favour of the corresponding ketones. 

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