| Abstract: | Photochemistry of Aminoketones. VIII. Diastereoselective Synthesis of 3-Hydroxy-prolines Glycine esters react in two steps (aminoalkylation and N-acylation) to N-acyl-N-(β-benzoylethyl)-glycine ester 3 . In less polar solvents these ketonic compounds are n,π*-excited by 300 nm irradiation. In ether 3 * yield mixtures of aminocyclopropanoles 4 , hydroxyprolines 5 and products of additions and cleavages. In benzene and cyclohexane/benzene, respectively, the regioselective photocyclization to 5 is favoured. Furthermore this hydroxyproline synthesis has the advantages of high diastereoselectivity yielding the ( 2,3) E–5 and of high overall-yields in connection with the one pot method. The influence of solvents and substituents on the regio- and diastereoselectivity are explained using a model with stabilization of special conformations of intermediates by dipol-dipol interactions. |
