Selective benzylic C-H monooxygenation mediated by iodine oxides

A method for the selective monooxdiation of secondary benzylic C-H bonds is described using an -oxyl catalyst and a hypervalent iodine species as a terminal oxidant. Combinations of ammonium iodate and catalytic -hydroxyphthalimide (NHPI) were shown to be effective in the selective oxidation of -but...

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Published inBeilstein journal of organic chemistry Vol. 15; no. 1; pp. 602 - 609
Main Authors LaMartina, Kelsey B, Kuck, Haley K, Oglesbee, Linda S, Al-Odaini, Asma, Boaz, Nicholas C
Format Journal Article
LanguageEnglish
Published Germany Beilstein-Institut 05.03.2019
Subjects
acetoxylation
benzylic
Chemistry
Full Research Paper
iodate
NHPI
oxidation
radical
oxidation
benzylic
iodate
radical
acetoxylation
NHPI
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Summary:A method for the selective monooxdiation of secondary benzylic C-H bonds is described using an -oxyl catalyst and a hypervalent iodine species as a terminal oxidant. Combinations of ammonium iodate and catalytic -hydroxyphthalimide (NHPI) were shown to be effective in the selective oxidation of -butylbenzene directly to 1-phenylbutyl acetate in high yield (86%). This method shows moderate substrate tolerance in the oxygenation of substrates containing secondary benzylic C-H bonds, yielding the corresponding benzylic acetates in good to moderate yield. Tertiary benzylic C-H bonds were shown to be unreactive under similar conditions, despite the weaker C-H bond. A preliminary mechanistic analysis suggests that this NHPI-iodate system is functioning by a radical-based mechanism where iodine generated in situ captures formed benzylic radicals. The benzylic iodide intermediate then solvolyzes to yield the product ester.
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ISSN:1860-5397
1860-5397
DOI:10.3762/bjoc.15.55