CRYSTAL AND MOLECULAR STRUCTURE OF 1,3-DIHYDRO-1-HYDROXY-3-OXO-1,2-BENZIODOXOLE

Benchtop-Stable Hypervalent Bromine(III) Compounds: Versatile Strategy and Platform for Air- and Moisture-Stable λ3-Bromanes

We present the first synthesis of air/moisture-stable λ³-bromanes (9 and 10) by using a cyclic 1,2-benzbromoxol-3-one (BBX) strategy. X-ray crystallography and NMR and IR spectroscopy of N-triflylimino-λ³-bromane (12) revealed that the bromine(III) center is effectively stabilized by intramolecular R-Br-O hypervalent bonding. This strategy enables the synthesis of a variety of air-, moisture-, and benchtop-stable Br-hydroxy, -acetoxy, -alkynyl, -aryl, and bis[(trifluoromethyl)sulfonyl]methylide λ³-bromane derivatives.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

Stoichiometric and catalytic oxidations with hypervalent organo-λ3-iodanes

Isolation, characterization, and reaction of the activated iodosylbenzene monomer, hydroxy(phenyl)iodonium ion, as a complex with 18-crown-6 (18C6) are reported. The reaction of iodosylbenzene with HBF(4) in the presence of 18C6 afforded the hydroxy-lambda(3)-iodane complex PhI(OH)BF(4).18C6 as stable yellow prisms. X-ray structure analysis indicated that the close contacts between the iodine(III) and the three adjacent oxygen atoms of 18C6 will be responsible for the increased stability of the complex compared to the uncomplexed PhI(OH)BF(4). The aqua complex of the activated iodosylbenzene, PhI(OH)OTf.18C6.H(2)O, with a water molecule coordinated to iodine(III) was also prepared. These crown ether complexes are highly reactive and serve as versatile stoichiometric oxidants, especially in water. Thus, the complexes undergo oxidative transformations of a variety of functional groups such as olefins, alkynes, enones, silyl enol ethers, sulfides, and phenols under mild conditions. The latter part reports on the iodobenzene-catalyzed alpha-oxidation of ketones, in which diacyloxy(phenyl)-lambda(3)-iodanes generated in situ act as real oxidants of ketones and m-chloroperbenzoic acid (m-CPBA) serves as a terminal oxidant. The oxidation of a ketone with m-CPBA in acetic acid in the presence of a catalytic amount of iodobenzene, BF(3)-Et(2)O, and water at room temperature affords an alpha-acetoxy ketone in good yield. It is noted that the use of water and BF(3)-Et(2)O is crucial to the success of this alpha-acetoxylation.

1-(Organosulfonyloxy)-3(1H)-1,2-benziodoxoles: Preparation and Reactions with Alkynyltrimethylsilanes

Organosulfonyloxy derivatives of 1,2-benziodoxol-3(1H)-one (3a-c) and 3,3-bis(trifluoromethyl)-3(1H)-1,2-benziodoxole (5a-c) can be prepared in high yield by the reaction of 1-hydroxybenziodoxoles 1 or 4 and the corresponding sulfonic acids or Me(3)SiOTf in the form of stable, but moderately hygroscopic, microcrystalline solids. Reaction of the triflate derivatives 3a and 5a with alkynyltrimethylsilanes affords either alkynyliodonium triflates 6, or (E)-beta-(trifluoromethanesulfonyloxy)alkenyliodonium triflates 7, while the same reaction in the presence of pyridine selectively gives the respective 1-alkynylbenziodoxoles 8 and 9 in 82-90% yield.