Phosphorescence of 8-azasteroids and related compounds.
We have investigated the electron absorption, fluorescence and phosphorescence spectra of 8-azasteroids and model compounds containing enaminodicarbonyl fragment. It has been shown that the investigated compounds have absorption and phosphorescence spectra similar in form and position. The results obtained permit the conclusion that the main deactivation channel of the excited singlet state is the intersystem crossing. It is suggested that the investigated 8-azasteroids of enaminodicarbonyl series under light irradiation undergo phototransformations presumably into derivatives with a gamma-pyridone fragment.
A Thioxanthone Sensitizer with a Chiral Phosphoric Acid Binding Site: Properties and Applications in Visible Light‐Mediated Cycloadditions
Abstract A chiral phosphoric acid with a 2,2’‐binaphthol core was prepared that displays two thioxanthone moieties at the 3,3’‐position as light‐harvesting antennas. Despite its relatively low triplet energy, the phosphoric acid was found to be an efficient catalyst for the enantioselective intermolecular [2+2] photocycloaddition of β‐carboxyl‐substituted cyclic enones (e.r. up to 93:7). Binding of the carboxylic acid to the sensitizer is suggested by NMR studies and by DFT calculations to occur by means of two hydrogen bonds. The binding event not only enables an enantioface differentiation but also modulates the triplet energy of the substrates.
Total Synthesis of 8-Azasteroids
Studies on the total synthesis of 8-azasteroids from the start of investigations in this field (1963) up to 1983 are examined. Earlier studies on the synthesis of compounds formally containing the 8-azasteroid skeleton and those on the synthesis of 8-azasteroids with an additional heteroatom are also analysed. Data are presented on the stereochemistry and biological activity of these compounds. The bibliography includes 148 references.