Nh

VNH2

QVo(CH2)2NEt2

hv EtOH

Et2N(CH2)20 Scheme 34

2.3.2 Blood pressure regulating drugs. The largely used 4-nitrophenyldihydropyridine vasodilators are quite photosensitive, as one may expect due to the copresence of the hydrogen abstracting nitro group and an easily abstractable benzylic hydrogen. Aromatisation of the heterocyclic ring and reduction of the nitro to the nitroso group result. In the presence of oxygen the nitroso function is in turn re-oxidised (see Scheme 35). Thus nifedipine (118a, R, R- Me) gives the corresponding nitrosophenylpyridine (119a), in part oxidised to the nitro derivative (120).120-122 Irradiation under oxygen gives directly the latter compound.123 The reaction occurs also in the solid state,124'125 and in this case clean formation of the nitroso derivative takes place (> 95%).126'127

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