4.5: Oxidation Reactions
Wacker-type tandem cyclization reaction of alkenyl alcohol is reported using chiral palladium(II)-spirobis(isoxazoline) with excellent enantioselectivity (Scheme \(\PageIndex{1}\)). In this reaction, benzoquinone reoxidizes the reduced palladium(0) to palladium(II) species to complete the catalytic cycle.
Palladium complex derived from Pd(TFA) 2 and ( S,S )-BOXAX has been found to be effective for the synthesis of chiral chroman framework in the presence of benzoquinone (Scheme \(\PageIndex{2}\)).
The mercury(II) complex derived from Hg(TFA) 2 and bisoxazoline has been used for the mercuriocyclization with high enantioselectivity (Scheme \(\PageIndex{3}\)).
Chiral cobalt(II)-salen has been used for the enantioselective intramolecular iodoetherification to procure 2-substituted tetrahydrofurans with up to 90% ee (Scheme \(\PageIndex{4}\)).