Low‐temperature Photcoxidation of Chlorophyll‐A*

Illumination of chlorophyll at low temperature, in solvents containing organic Lewis bases and oxygen, leads to oxidation of the C‐2 vinyl group. This oxidation proceeds through a series of thermal and photochemical changes, including initial formation of a new compound (I) absorbing at 620 nm. This undergoes further rapid photochemical (or thermal) conversion back to a chlorin‐like substance (II), and much slower phototransformation to a third intermediate (III) absorbing near 500 nm. The reaction requires complexed metal (Mg or Zn), but not an intact cyclopentanone ring. The ‘620’ photoproduct is assigned to a cyclic peroxide involving C‐1 of chlorophyll and the vinyl group.