Propentdyopents and related compounds. Part 4. Propentdyopent–alkanol adducts by the photo-oxygenation of pyrromethenones
Abstract
Photo-oxygenation of tetraethylpyrromethenone and of tetramethylpyrromethenone in methanol in the presence of oxygen and a porphyrin photosensitises gives the corresponding methanol–propentdyopent adducts in good yields. The photo-oxygenation reaction is shown not to be a satisfactory route to the analogous adducts with ethanol, propanol and butanol, but these compounds can be prepared by the acid-catalysed alcoholysis of the zinc(II) bis(tetra-alkylpropentdyopent) complexes. The photooxygenation is applied to [meso-13C]tetraethylpyrromethenone, and the result confirms the formulation of the methanol–propentdyopents as valley methoxy derivatives.