Wu J.-D, Tosaka M, Kayahara E, Mizuhata Y, Yamago S. 

Journal of Organic Chemistry (2026)

The ortho-nitrobenzyl (oNB) group is among the most widely used photodegradable units, serving in diverse fields, including its use as a protective group in organic synthesis, as a stimulus in photoresponsive and photodegradable polymer materials, and in caged molecules in biology. Despite its extensive application, however, little is known about the fate of the photodegraded fragments of the oNB group and their potential impact on the system in which they are used. Here, we isolated o-nitrosobenzaldehyde (2), a proposed primary photoadduct of the oNB group, and investigated its stability and reactivity. Compound 2 rapidly decomposed under both thermal and photochemical conditions, forming oligomers bearing azo- and amide-linkages. The structure of a trimer containing both linkages was unambiguously determined by single-crystal X-ray diffraction. We further found that dienes effectively trapped the nitroso group in 2 by the hetero-Diels–Alder reaction, thereby minimizing undesired oligomerization. This trapping strategy, in combination with a microflow reaction system, significantly enhances the photodegradation efficiency of the oNB-containing polymers. These findings shed new light on the photochemistry of oNB groups and provide a rational basis for the design and implementation of oNB groups in advanced functional systems.