L-prolinoyl chiral picket iron porphyrins evaluated for the enantioselective epoxidation of alkenes

Four atropisomers of an L-prolinoyl picket porphyrin were synthesised from tetra-o-aminophenyl porphyrin (TAPP) and were evaluated as alkene epoxidation catalysts after incorporation of iron in the porphyrin core. In the case of the alphaalphaalphaalpha atropisomer bearing the four amino groups on the same side, a bulky base was employed in order to suppress the eventual reaction on the non-functionalised side of the porphyrin. The resulting enantioselectivities were compared with either other chiral motifs or with the corresponding strapped porphyrins. The enantioselectivities obtained with picket porphyrins are as high as those for strapped porphryins, and in some cases, even higher.