The synthetic utility and mechanisms of the hydrogen iodide isomerization and the oxo reaction in the modification of chlorophyll derivatives

✍ Scribed by Hynninen, Paavo H.

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 612 KB
• Volume: 1990
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1990199001157

✦ Synopsis

Abstract

Hydrogen iodide in glacial acetic acid has served as a versatile reagent in modifications of chlorophyll and its closely related derivatives, e.g. pheophorbides and 3‐vinylchlorins, to 3‐ethyl‐porphyrins (HI isomerization) or to 3^1^‐oxoporphyrins (oxo reaction). Nevertheless, the mechamisms of these important reactions have remained obscure. In this paper, the reaction conditions used by H. Fischer for the HI isomerization and the oxo reaction are first thoroughly examined. Secondly, a carbocation rearrangement mechanism is suggested for the HI isomerization. Thirdly, the oxo reaction is rationalized by means of a reaction between a chlorin 3^1^‐carbocation and water nucleophile and subsequent dehydrogenation by triplet oxygen. Finally, some related unsolved problems of chlorophyll chemistry are briefly discussed.