Sweet chiral porphyrins as singlet oxygen sensitizers for asymmetric Type II photooxygenation

Carbohydrate-decorated meso-tetraarylporphyrins P-G and P-C were synthesized via Lewis-acid catalyzed condensation of acetylated carbohydrate-substituted benzaldehydes and pyrrole. Their efficiency of singlet oxygen production was compared with the corresponding non-substituted porphyrin. The oxidation of the spin trap molecule TEMP (2,2,6,6-tetramethyl-4-piperidone) by singlet oxygen to TEMPO was measured by ESR spectroscopy, showing higher reaction rates for the sugar porphyrins. These results were corroborate by laser flash photolysis measurements that resulted in higher triplet lifetimes of glucosyl-and cellobiosyl porphyrins in comparison with tetrakis(4-hydroxyphenyl) porphyrin. Low ee was detected in the photooxygenation of ethyl tiglate.