Reactions of Protoporphyrin with Tetracyanoethylene
DiNello, R.K. and David Dolphin
J. Org. Chem.
The vinyl groups of protoporphyrin react with tetracyanoethylene (TCNE) in a [2 + 2] reaction to give adducts containing one and two cyclobutane rings, e.g. I. In addition, the vinyl groups and the porphyrinic β-β cross-conjugated double bonds in rings A and B react with TCNE in a [4 + 2] cycloaddition reaction, giving chlorins when either ring A or B reacts or an isobacteriochlorin when both rings react. Reactions in which one vinyl group reacted in a [2 + 2] and the other in a [4 + 2] fashion were also observed.