A simple synthesis of functionalized rac‐chlorins via allylboration of porphyrin aldehydes

Chlorins rac‐17a, b which bear terminally hydroxy‐substituted butyl side chains were synthesized by allylboration and Claisen rearrangement from readily accessible formylporphyrins 5 and 6. The hydroxyalkyl side chain and the photo‐physical properties of the chlorins rac‐17a, b should open a broad access to chlorins suitable for photodynamic therapy having different residues attached to the hydroxy function. The reported synthetic pathway also should be useful for the synthesis of naturally occurring hydroporphyrins containing geminally dialkylated structural parts and a propionic acid residue on the saturated pyrrole ring.