Oxidation with chromium(VI) complexes: Difference between revisions

Revision as of 18:26, 9 June 2025

Latest revision as of 10:56, 23 July 2025

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==Scope and limitations==

Buffering agents may be used to prevent acid-labile protecting groups from being removed during chromium(VI)-amine oxidations. However, buffers will also slow down oxidative cyclizations, leading to selective oxidation of alcohols over any other sort of oxidative transformation. Citronellol, for instance, which cyclizes to pugellols in the presence of PCC, does not undergo cyclization when buffers are used.<ref>Fieser, L. F.; Fieser, M. ''Reagents for Organic Synthesis''; Wiley-Interscience, New York, 1979, '''7''', 309.</ref><ref name=whatup>{{cite journal|title=A Facile Method for the Bishomologation of Ketones to α,β-Unsaturated Aldehydes: Application to the Synthesis of the Cyclohexanoid Components of the Boll Weevil Sex Attractant

|author=James H. Babler, Michael J. Coghlan|pagepages= 469-474469–474|year= 2007|doi=10.1080/00397917608082626|journal=Synthetic Communications}}</ref>

{{center|[[File:ChroScope1.png]]}}

Oxidative cyclization can be used to prepare substituted tetrahydrofurans. Cyclization of dienols leads to the formation of two tetrahydrofuran rings in a ''syn'' fashion.<ref name=OR/>

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==Comparison with other methods==

Methods employing dimethyl sulfoxide (the [[Swern oxidation|Swern]] and [[Moffatt oxidation]]s) are superior to chromium(VI)-amines for oxidations of substrates with heteroatom functionality that may coordinate to chromium.<ref>Tidwell, T. ''Org. React.'' '''1990''', ''39'', 297.</ref> [[Dess-Martin periodinane]] (DMP) offers the advantages of operational simplicity, a lack of heavy metal byproducts, and selective oxidation of complex, late-stage synthetic intermediates.<ref>{{cite journalbook |doi=10.1002/047084289X.rt157m.pub2|titlechapter=1,1,1-Triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one|journaltitle=Encyclopedia of Reagents for Organic Synthesis|year=2009|last1=Boeckman|first1=Robert J.|last2=George|first2=Kelly M.|isbn=978-0471936237 }}</ref> Additionally, both DMP and [[manganese dioxide]] (MnO₂) can be used to oxidize allylic alcohols to the corresponding enones without allylic transposition. When allylic transpositions is desired, however, chromium(VI)-amine reagents are unrivaled.

Catalytic methods employing cheap, clean terminal oxidants in conjunction with catalytic amounts of chromium reagents produce only small amounts of metal byproducts.<ref name=OR/> However, undesired side reactions mediated by stoichiometric amounts of the terminal oxidant may occur.