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The synthetic utility and mechanisms of the hydrogen iodide isomerization and the oxo reaction in the modification of chlorophyll derivatives
Author(s) -
Hynninen Paavo H.
Publication year - 1990
Publication title -
liebigs annalen der chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0170-2041
DOI - 10.1002/jlac.1990199001157
Subject(s) - chemistry , isomerization , carbocation , dehydrogenation , photochemistry , nucleophile , iodide , reagent , reaction mechanism , methyl iodide , acetic acid , hydrogen , medicinal chemistry , organic chemistry , catalysis
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.