Research on photochemical transformations of terarylenes containing an allomaltol fragment are ongoing at the ZIOC

Photochemical processes are a powerful tool widely used in organic synthesis. However, despite the obvious advantages of photochemical synthesis methods, a significant limitation is the regioselectivity of these processes. For example, the direction of the photoreaction is difficult to predict if there are two fragments in the molecule capable of phototransformation. UV irradiation of such compounds can lead to the formation of a complex mixture of products, which greatly complicates the effective use of photoreactions for such objects.

As part of the ongoing research by researchers from the Laboratory of Heterocyclic Compounds of the Zelinsky Institute in the field of photoinduced transformations of terarylenes, the photochemical reaction of substituted oxazole-2 (3H)-ones containing an allomaltol fragment was studied. On one hand, under the action of UV irradiation, these compounds undergo classical 6π-electrocyclization of the 1,3,5-hexatriene system with the formation of polycyclic systems. At the same time, as was shown earlier, the allomaltol fragment upon exposure to UV light can transform into an unstable α-hydroxydiketone intermediate as a result of the contraction of the pyranone ring. That is why theoretical prediction of the phototransformation path for such objects is a difficult task. Initially, UV irradiation of terarylenes containing an allomaltol fragment resulted in the formation of a complex mixture of inseparable products. It was found that the alkylation of the hydroxy group in the 3d position of the pyranone ring completely excludes the photoreaction with the participation of the allomaltol fragment by blocking the process of intramolecular proton transfer in the excited state. Subsequent irradiation of such systems made it possible to synthesize a previously unknown class of compounds — benzo [5,6] chromeno [8,7-d] oxazole-2,7(3H)-diones. It was also shown that the detected photocyclization of substituted oxazol-2-ones can be used for the photogeneration of biologically active alcohols, for example, choline iodide and various acids, including the non-steroidal anti-inflammatory drug (S)-naproxen.

Source:

Andrey N. Komogortsev, Boris V. Lichitsky, Valeriya G. Melekhina, Darina I. Nasyrova, Constantine V. Milyutin. Photoinduced 6π-Electrocyclization of a 1,3,5-Hexatriene System Containing an Allomaltol Fragment. J. Org. Chem. 2021,  accepted manuscript. DOI: 10.1021/acs.joc.1c01902