Nitro group photoreduction of 4-(2-nitrophenyl)- and 4-(3-nitrophenyl)-1,4-dihydropyridines

Modelling nifedipine photodegradation, photostability and actinometric properties

“…The photoconversion of NIF leads to a nitroso (PP) derivative (Piechocki and Thoma, 2010;Tonnesen, 2004;Albini and Fasani, 1998;Pietta et al, 1981;Fasani et al, 2006;Gorner, 2010) according to Scheme 1. Albini and Fasani (1998) reported that the nitroso derivative might be converted into a nitro derivative through a thermal re-oxidation.…”

“…A number of kinetic methods have been proposed to study the photodecomposition of NIF (Piechocki and Thoma, 2010;Tonnesen, 2004;Albini and Fasani, 1998;Pietta et al, 1981;Fasani et al, 2006;Gorner, 2010). Separation techniques were largely preferred because they allow monitoring the kinetic evolution of NIF concentration throughout the photodegradtion reaction.…”

Efficient Photooxidation of Aryl(hetaryl)pyrazolines by Benzoquinone

“…Meanwhile, examples of successful photochemical oxidation of dihydrohetarenes are also available. 3‐Acetyl‐3,4‐dihydrocoumarin , dihydropyridines and arylpyrazolines have been photooxidized effectively. It is important that some of the photochemical procedures provide high yields of the corresponding hetarenes .…”

Substituent Effect on the Photolability of 4‐Aryl‐1,4‐Dihydropyridines

“…15% in the presence of oxygen (23). It is reassuring that G€ orner (24), recently described the contribution of the triplet state to the photodegradation of NIMO. Evidence of the NIMO triplet excited state participation was also established in a previous work (26).…”

“…Only a minor participation of triplet excited state could be expected on the basis of the low O 2 ( 1 D g ) generation quantum yield and the lack of any transient absorption in the laser flash photolysis experiments. In fact, a weak triplet state formation has been observed and reported for compounds bearing 3-nitrophenyl substituents (24). Depending on the energy of the zwitterionic biradical, it could evolve (back electron transfer) to the ground state or to two different triplet species, located either in the aromatic moiety (DHP-3 Ar) or in the dihydropyridine ring ( 3 DHP-Ar) (22), our results indicate that for the studied compounds the energy of zwitterionic biradical is below both triplets, therefore back electron should regenerate the ground-state reactants.…”