Active hydrogen reaction with nitrenes

The most popular type of photosensitive functionality is the aryl azide derivative. On photolysis, phenyl azide groups form short-lived nitrenes that react rapidly with the surrounding chemical environment (Gilchrist and Rees, 1969). Nitrenes can insert nonspecifically into chemical bonds of target molecules, including undergoing addition reactions with double bonds and insertion reactions into active hydrogen bonds at l"l C—H and N—H sites. Abundant evidence, however, indicates that the photolyzed... 

Figure 5.16 Photoactivation of a phenyl azide group with UV light results in the formation of a short-lived nitrene. Nitrenes may undergo a number of reactions, including insertion into active carbon-hydrogen or nitrogen-hydrogen bonds and addition to points of unsaturation in carbon chains. The most likely route of reaction, however, is to ring-expand to a dehydroazepine intermediate. This group is highly reactive toward nucleophiles, especially amines.

The first chemists working in the area of the carbonylation of nitro compounds immediately noted many similarities between the products obtained from these reactions and the ones obtained from the reactions of organic azides (R-N3), which were known to be sources of free nitrenes when activated either photochemically or thermally (for some examples see [255, 256]). Similarities were especially found in the formation of coupled products such as azoarenes and in the formation of products derived from hydrogen-abstraction from the solvent or the nitro compound itself [255], a reaction typical for nitrenes in the triplet state [257]. It was also noted that high pressures were required to drive the reactions of both azides and nitro compounds with CO towards the synthesis of isocyanates rather than towards hydrogen-abstraction-derived products and this... 

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