A two-step, one-pot route to swap the pyrroline moiety in meso-tetraaryldihydroxy-chlorins with an O/N-substituted oxazoline

Reaction of diolchlorins—made from meso-tetraarylporphyrins by OsO4-mediated oxidation—with NaIO4 on silica gel in the presence of a secondary amine or alcohol, followed by MnO4−-induced oxidation, leads to the replacement of a pyrroline β-carbon with oxygen to form α-substituted oxazolochlorin aminals or acetals, respectively. This two-step, one-pot reaction is a significant improvement over existing methods to prepare the oxazoline-based porphyrinoids. The number of steps is reduced from 5 to 2 and the overall yields more than doubled to 33–86%. The reaction also allows the preparation of oxazolochlorins carrying meso-substituents that are incompatible with existing methods. Lastly, the reaction further highlights the reactivity of morpholino-chlorins and provides further clues as to the mechanism of the intriguing carbon-to-oxygen atom swap reaction step in the current reaction, as well as in previously observed reactions.