Insertion reactions photochemical

En gros, the N insertion reactions can be subdivided into a Beckmann type and a Schmidt-type rearrangement part. Furthermore, some photochemical rearrangements of chiral oxaziridines are known to generate a range of optically active lactams. 

The photoelimination of nitrogen from diazo compounds provides a simple and versatile route for the generation of carbenes, and in certain instances, insertion reactions of carbenes can be employed in the synthesis of heterocycles. Carbenes are believed to be involved at least in part in the photochemically induced conversion of N,N-diethyldiazoacetamide (439) into the y-lactam 440 and the /Mactam 441,365 and a similar approach has been successfully employed in the synthesis of a carbapen-2-em366 and of 7-methylcephalosporin analogues.367 Carbene insertion of a different type has been observed on irradiation of the 6-anilino-5-diazouracils 442 to give the indolo[2,3-d]pyrimidines 443.368 Ring contractions in heterocycles... 

The fact that both the thermal and the photochemical insertion reactions yield the same products via formation of charge-transfer complexes leads to the conclusion that the reactive ion-radical pair in equation (52) is the common intermediate for both activation processes. Such a conclusion is further verified by the direct observation of anion-radical intermediates from the thermal reaction of TCNE and DDQ with various metal hydrides.188... 

The photochemistry of aryl azides is quite complex, suggesting that the nitrene 14 may not be the only reactive intermediate and that insertion reactions may not be the only route to form photoconjugates.Although aryl nitrenes are much less susceptible to rearrangements than acyl nitrenes, they may still occur and lead to the formation of reactive intermediates such as azepines, which may go on to react with nucleophiles.[911 141 Addition of nitrenes to double bonds will generate azirines, while dimerization will produce azobenzenesJ11 Aryl azides are stable to most of the procedures used in the course of peptide synthesis except for reduction reactions. Non-photochemical reduction of aryl azides to the primary amines by thiols has been reported by Staros et al.[15]... 

Luminescence is seldom observed from free radicals and radical ions because of the low energy of the lowest excited states of open-shell species, the benzophenone ketyl radical being however a noteworthy exception. There are few reports of actual photochemical reactions of free radicals, but the situation is different with biradicals such as carbenes. These have two unpaired electrons and can exist in singlet or triplet states and they take part in addition and insertion reactions (Figure 4.90). 

Photochemical or copper-catalyzed decomposition of diazo compound 85 failed to give a handle on 2-silanaphthalene 87 (equation 19)49,50. Instead of the expected 1,2-Ph migration, carbene 86 apparently underwent simply an 0,H insertion reaction with methanol in 96% yield. 

Recently, Kistiakowsky and co-workers8 found that reactions of methylene, formed by photochemical decomposition of ketene or diazomethane, produce hydrocarbon molecules with considerable excess vibrational energy. The C—H insertion reaction is represented by reaction (3) ... 

The second category includes reactions in which the simultaneous formation of two carbon-carbon bonds completes the framework of the bicyclobutane moiety. For the sake of simplicity, carbene insertion reactions as well as some photochemical transformations are considered in this context as being concerted reactions . 

With respect to carbonylation chemistry Sakakura and Tanaka have shown that irridiation of rhodium complex RhCl(CO)(PMe3)2 in pentane as solvent under a CO atmosphere (1 bar) at ambient temperature gives rise to carbonylated products. Selectivity for linear aldehyde is > 98 % (eq. (11)) [45]. This insertion reaction is photochemically driven, since it is known that aldehyde decarbonylation is a thermodynamically favorable process. Other photochemial C-H activation reactions have been investigated [46]. When toluene is reacted in the presence of CO and the same Rh complex, phenyl acetaldehyde is obtained as the major product (eq. (12)) [47]. 

C-H carbene insertion reactions. Hydrogen abstraction products were formed at the expense of insertion products on irradiation of -nitrophenyldiazomethane under the same conditions. Possible explanations for this difference in reactivity have been offered. Photochemically generated aryl carbenes have been intercepted with carbon monoxide and with oxygen. Benzophenone 0-oxide has been detected spectroscopically on irradiation (515 nm) of diphenyl-... 

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