PhI- and polymer-supported PhI-catalyzed oxidative conversion of ketones and alcohols to α-tosyloxyketones with m-chloroperbenzoic acid and p-toluenesulfonic acid

p-TsOH-Catalyzed one-pot transformation of di- and trihydroxy steroids towards diverse A/B-ring oxo-functionalization

A milder, facile, and greener transformative protocol, specifically on solid supports, to yield A-ring and/or B-ring oxo-functionalized steroids has been accomplished.

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.

Relative Rate Profiles of Functionalized Iodoarene Catalysts for Iodine(III) Oxidations

A series of rate studies were conducted to evaluate the steric and electronic properties that govern the reactivity of iodoarene amide catalysts in the α-oxytosylation of propiophenone. A meta-substituted benzamide catalyst emerged as the most reactive. This catalyst was employed in the α-oxytosylation of a series of substituted propiophenones, returning the α-tosyloxy ketone products in excellent isolated yield.

Cross-dehydrogenative coupling for the intermolecular C-O bond formation

The present review summarizes primary publications on the cross-dehydrogenative C-O coupling, with special emphasis on the studies published after 2000. The starting compound, which donates a carbon atom for the formation of a new C-O bond, is called the CH-reagent or the C-reagent, and the compound, an oxygen atom of which is involved in the new bond, is called the OH-reagent or the O-reagent. Alcohols and carboxylic acids are most commonly used as O-reagents; hydroxylamine derivatives, hydroperoxides, and sulfonic acids are employed less often. The cross-dehydrogenative C-O coupling reactions are carried out using different C-reagents, such as compounds containing directing functional groups (amide, heteroaromatic, oxime, and so on) and compounds with activated C-H bonds (aldehydes, alcohols, ketones, ethers, amines, amides, compounds containing the benzyl, allyl, or propargyl moiety). An analysis of the published data showed that the principles at the basis of a particular cross-dehydrogenative C-O coupling reaction are dictated mainly by the nature of the C-reagent. Hence, in the present review the data are classified according to the structures of C-reagents, and, in the second place, according to the type of oxidative systems. Besides the typical cross-dehydrogenative coupling reactions of CH- and OH-reagents, closely related C-H activation processes involving intermolecular C-O bond formation are discussed: acyloxylation reactions with ArI(O2CR)2 reagents and generation of O-reagents in situ from C-reagents (methylarenes, aldehydes, etc.).

Hypervalent iodine-catalyzed oxidative functionalizations including stereoselective reactions

Hypervalent iodine chemistry is now a well-established area of organic chemistry. Novel hypervalent iodine reagents have been introduced in many different transformations owing to their mild reaction conditions and environmentally friendly nature. Recently, these reagents have received particular attention because of their applications in catalysis. Numerous hypervalent iodine-catalyzed oxidative functionalizations such as oxidations of various alcohols and phenols, α-functionalizations of carbonyl compounds, cyclizations, and rearrangements have been developed successfully. In these catalytic reactions stoichiometric oxidants such as mCPBA or oxone play a crucial role to generate the iodine(III) or iodine(V) species in situ. In this Focus Review, recent developments of hypervalent iodine-catalyzed reactions are described including some asymmetric variants. Catalytic reactions using recyclable hypervalent iodine catalysts are also covered.

meta-Chloroperbenzoic acid (mCPBA): a versatile reagent in organic synthesis

This review aims to collect and discuss the synthetic applications of meta-chloroperbenzoic acid (mCPBA) over the past few decades.

An Iodobenzene-Catalysed Domino Route toward Quinoxaline Derivatives from Simple Ketones and o-Phenylenediamines in One Pot

An iodobenzene-catalysed domino route to quinoxalines from ketones and o-phenylenediamines in one pot has been developed. This transformation consisted of the generation of Koser's generation, α-tosyloxylation of ketones, nucleophilic substitution and intramolecular dehydration with o-phenylenediamines, and dehydrogenation.

Catalytic hypervalent iodine oxidation of alcohols to the corresponding carbonyl compounds using N-hydroxyphthalimide (NHPI) and m-chloroperbenzoic acid

An efficient, facile, and mild oxidation of alcohols to the corresponding carbonyl compounds with m-chloroperbenzoic acid (mCPBA) and N-hydroxyphthalimide (NHPI) in the presence of a catalytic amount of iodobenzene was reported. The oxidation proceeded in mixed solvent at room temperature to afford carbonyl compounds in excellent yields. A possible mechanism for the oxidation was proposed.

α-Tosyloxylation of ketones with ion-supported[hydroxy(tosyloxy)iodo] benzene

A new room-temperature ionic liquid (RTIL) supported [hydroxy(tosyloxy)iodo]benzene (ion-supported HTIB) reagent was synthesised by three kinds of effective methods in high yields, which combined the advantages of ionic liquids and the hypervalent iodine. Ion-supported HTIB was an effective reagent for one-step conversion of ketones to the corresponding α-tosyloxylated ketones in the ionic liquid [emim]BF4or acetonitrile under microwave. After the conversion reaction, the reagent was transformed into ion-supported iodobenzene, which could be recovered and regenerated easily without lost of activity.

Catalytic hypervalent iodine oxidation using 4-iodophenoxyacetic acid and oxone: oxidation of p-alkoxyphenols to p-benzoquinones

A catalytic hypervalent iodine oxidation of p-alkoxyphenols using 4-iodophenoxyacetic acid (1a) and Oxone((R)) was developed. Reaction of p-alkoxyphenol (2) with a catalytic amount of 1a in the presence of Oxone((R)) as a co-oxidant in 2,2,2-trifluoroethanol-water (1 : 2) gave the corresponding p-quinone (3) in excellent yield without special operation. The substituent effect on iodobenzene ring in the oxidation was observed; p-alkoxy is the most effective, with the series following the approximate order p-RO>p-Me, o-MeO, m-MeO>H>o-CO(2)H. And remarkable solvent effects were observed.

Hypervalent iodine reagents as a new entrance to organocatalysts

The catalytic utilization of hypervalent iodine reagents, largely in consideration of economical and environmental viewpoints, is a most attractive strategy due to their unique features as extremely useful oxidants, with mild, safe, and environmentally friendly characteristics. In addition to a system based on electrochemical reoxidation conditions, new reliable catalytic methods have emerged in recent years that can broaden the scope of the catalytic concept. For these contributions, a catalytic strategy is now available for performing many representative types of oxidative bond-forming reactions and alcohol oxidations mediated by hypervalent iodines, some of which even include key transformations for natural product synthesis. A suitable choice of terminal oxidants, e.g., m-chloroperbenzoic acid (mCPBA) or Oxone, for generation of active hypervalent iodine(iii) or (v) species from iodoarenes in situ, has led to recent rapid expansion in this field. This feature article highlights the historical background and the efforts made to realize the catalytic utilization of these reagents, especially with focus on iodine(iii).

Catalytic hypervalent iodine oxidation of p-dialkoxybenzenes to p-quinones using 4-iodophenoxyacetic acid and Oxone

A catalytic hypervalent iodine oxidation of p-dialkoxybenzenes using 4-iodophenoxyacetic acid (1) and 2KHSO5 x KHSO4 x K2SO4 (Oxone) was developed. Reaction of p-dialkoxybenzenes (2) with a catalytic amount of 1 in the presence of Oxone as a co-oxidant in 2,2,2-trifluoroethanol-water (1 : 2) gave the corresponding p-quinones (3) in excellent yields without purification. This procedure was applied to synthesis of blattellaquinone (9), the sex pheromone of the German cockroach, Blattella germanica.

A new H2O2/acid anhydride system for the iodoarene-catalyzed C-C bond-forming reactions of phenols

We have succeeded in the first versatile iodoarene-catalyzed C-C bond-forming reactions by development of a new reoxidation system at low temperatures using stoichiometric bis(trifluoroacetyl) peroxide A in 2,2,2-trifluoroethanol (TFE). The catalytic system supplies a wide range of substrates and functional availabilities sufficient to be used in the key synthetic process of producing biologically important Amaryllidaceae alkaloids.

Catalytic oxidation of organic substrates by molecular oxygen and hydrogen peroxide by multistep electron transfer--a biomimetic approach

Oxidation reactions are of fundamental importance in nature, and are key transformations in organic synthesis. The development of new processes that employ transition metals as substrate-selective catalysts and stoichiometric environmentally friendly oxidants, such as molecular oxygen or hydrogen peroxide, is one of the most important goals in oxidation chemistry. Direct oxidation of the catalyst by molecular oxygen or hydrogen peroxide is often kinetically unfavored. The use of coupled catalytic systems with electron-transfer mediators (ETMs) usually facilitates the procedures by transporting the electrons from the catalyst to the oxidant along a low-energy pathway, thereby increasing the efficiency of the oxidation and thus complementing the direct oxidation reactions. As a result of the similarities with biological systems, this can be dubbed a biomimetic approach.