Development and Application of New Oxidation Systems Utilizing Oxometalate Catalysts

Abstract

This review describes our recent efforts in the development and application of new oxidation systems utilizing oxometalate catalysts. The novel use of heteropoly acid (HPA), an acidic oxometalate catalyst, in hypervalent iodine-mediated oxidations provided an effective strategy to generate cation radical species that enables a variety of direct C-H functionalizations of aromatic compounds. This strategy brought a facile biaryl synthesis and new spirodienone syntheses in aromatic oxidation chemistry. Moreover, this strategy opens up a facile synthetic route to morphinandienone alkaloids. On the other hand, the use of oxometalate catalyst together with poly(N-isopropylacrylamide) (PNIPAAm)-based polymer in the development of new solid-phase catalyst provided a novel reaction system in water. Due to the characteristic temperature-responsive intelligence of PNIPAAm, this reaction system brought a remarkable acceleration of the reactivity and ease of catalyst recovering in catalytic oxidation that uses hydrogen peroxide or oxygen gas (O 2 ) as primary oxidant. In addition, the recovered solid-phase catalyst could be used for consecutive reactions without any significant loss of its catalytic efficacy.

Asymmetric Synthesis of Gonytolide A: Strategic Use of an Aryl Halide Blocking Group for Oxidative Coupling

“…In line with literature precedents and on the basis of the need for a blocking group and the reactivity observed with O -methylated substrate 21 , we propose that the oxidative dimerization may proceed through nucleophilic addition of 10 to an electrophilic radical cation (Figure ). We propose that the o -bromide 10 may be oxidized by VOF 3 /TFA/TFAA to form a phenoxyl radical cation ( 22 ), likely through a charge transfer complex . The o -bromine may potentially stabilize the radical cation through electronic effects.…”

“…We propose that the ortho -bromide 10 may be oxidized by VOF 3 /TFA/TFAA to form a phenoxyl radical cation 22 , likely through a charge transfer complex. 36 The ortho -bromine may potentially stabilize the radical cation through electronic effects. Moreover, calculations 5,37 support such stabilization effects by showing that the spin density can reside on the bromine atom of 22 .…”

“…We propose that the o-bromide 10 may be oxidized by VOF 3 /TFA/TFAA to form a phenoxyl radical cation (22), likely through a charge transfer complex. 36 The o-bromine may potentially stabilize the radical cation through electronic effects. Moreover, calculations 5,37 We further considered that atropdiastereoselection for production of either 26 or 27 may be thermodynamically controlled by the relative energies of cyclohexadienone intermediates 24 and 25.…”

Tandem Oxidative α-Hydroxylation/β-Acetalization Reaction of β-Ketoamides and Its Applications

“…Organoiodine reagents, possessing reactivity similar to that of transition metals, are widely used in various organic reactions as selective oxidants and environmentally friendly reagents, including aminations, oxidations, halogenations, C–C bond-forming reactions, rearrangements, and transition-metal-catalyzed reactions. − They are also used for the acetalization of carbonyl compounds. , In 2005, in a perspective of Moriarty group’s work in hypervalent iodine chemistry, it was reported that the alcoholysis of iodobenzene diacetate (PIDA: PhI­(OAc) 2 ) in MeOH can generate the active reagent (dimethoxyiodo)­benzene (PhI­(OMe) 2 ) . The concomitantly formed enolate anion 1′ subsequently adds to the PhI­(OMe) 2 to yield intermediate A , which results in intermediate B via the addition of a methoxide anion.…”