Premium
Product Analysis in the Iodine(III)‐Promoted Oxidation of Carbohydrate‐Derived Cyclic Enol Ethers: A Mechanistic Study
Author(s) -
Harders Jan,
Garming Alfons,
Jung Alexander,
Kaiser Volker,
Monenschein Holger,
Ries Monika,
Rose Lars,
Schöning KaiUwe,
Weber Thomas,
Kirschning Andreas
Publication year - 1997
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199719971015
Subject(s) - chemistry , glycal , hypervalent molecule , iodobenzene , enol , iodine , reagent , electrophile , organic chemistry , enol ether , pyran , medicinal chemistry , stereochemistry , catalysis , stereoselectivity
A study on the mechanism of the well‐documented hypervalent iodine‐mediated allylic oxidation of glycals leading to 2,3‐dihydro‐4 H ‐pyran‐4‐ones is presented. Notable features are the isolation of ring‐contracted by‐products 6 and 7 , which are produced upon oxidation of per‐ O ‐benzylated glycal 4 , as well as the characterization of carbohydrate‐derived tetrahydrofurfurals 12a and 13a , which are formed by the conformation‐dependent oxidation of glycals 9a and 10b . In addition, the iodine(III)‐mediated oxidation process has been studied by in situ NMR spectroscopy of lyxo ‐configured glycals 14a,b . Intermediate alkylphenyliodonium species 19b,d and 2‐enoyranosides 16a and 20a have been characterized by their NMR signals. These data support a plausible mechanism that is initiated by electrophilic attack of the iodine(III) reagent on the electron‐rich enol ether double bond of the glycal. This is followed by the breaking of a bond β,γ‐positioned in relation to the carbohydrate‐bound iodine and subsequent reductive elimination of iodobenzene. Thus, depending on the glycals employed, a number of diverse oxidation products may be formed.