Unified strategy for iodine(III)-mediated halogenation and azidation of 1,3-dicarbonyl compounds

Isolation and Biomimetic Semisynthesis of Hyperzrones A and B, Two Nor-Polycyclic Polyprenylated Acylphloroglucinols with a Characteristic Cyclobutane Moiety, from Hypericum beanii

Hyperzrones A (1) and B (2), two unprecedented nor-polycyclic polyprenylated acylphloroglucinols with a characteristic cyclobutane moiety, were discovered from Hypericum beanii. Their structures were determined by extensive spectroscopic analysis, X-ray crystallography, and quantum chemical calculation methods. A bioinspired semisynthesis of 1 and 2 was achieved from the natural precursor hypercalin B (3), featuring a Favorskii-type rearrangement and a visible-light-mediated [2 + 2] photocycloaddition. Several diverse derivatives were also obtained, providing a compound library for biological studies.

Tetrabutylammonium iodide-catalyzed oxidative α-azidation of β-ketocarbonyl compounds using sodium azide

We herein report the oxidative α-azidation of carbonyl compounds by using NaN3 in the presence of dibenzoyl peroxide catalyzed by tetrabutylammonium iodide (TBAI). By utilizing these readily available bulk chemicals a variety of cyclic β-ketocarbonyl derivatives can be efficiently α-azidated under operationally simple conditions. Control experiments support a mechanistic scenario involving in situ formation of an ammonium hypoiodite species which first facilitates the α-iodination of the pronucleophile, followed by a phase-transfer-catalyzed nucleophilic substitution by the azide. Furthermore, we also show that an analogous α-nitration by using NaNO2 under otherwise identical conditions is possible as well.

Total Synthesis of (±)-Oxacyclododecindione

Racemic total synthesis of the natural product oxacyclododecindione, isolated in 2008 as the first member of the oxacyclododecindione family, is reported. Studies toward this molecule commenced with a biomimetic late-stage C-H oxidation starting from 14-deoxyoxacyclododecindione as a known precursor. This provided insights into the reactivity of the macrolactone class but did not permit the synthesis of the target natural product. Based on these results, a synthetic strategy through intramolecular Friedel-Crafts acylation combined with Barton decarboxylation to introduce the tertiary alcohol, a major challenge in previous synthetic efforts, was envisioned. This resulted in an 11-step racemic total synthesis of (±)-oxacyclododecindione, renowned for its potent anti-inflammatory and antifibrotic activities.

An α-Cyclopropanation of Carbonyl Derivatives by Oxidative Umpolung

The reactivity of iodine(III) reagents towards nucleophiles is often associated with umpolung and cationic mechanisms. Herein, we report a general process converting a range of ketone derivatives into α-cyclopropanated ketones by oxidative umpolung. Mechanistic investigation and careful characterization of side products revealed that the reaction follows an unexpected pathway and suggests the intermediacy of non-classical carbocations.

Safer Synthesis of (Diacetoxyiodo)arenes Using Sodium Hypochlorite Pentahydrate

A practical method for the preparation of (diacetoxyiodo)arene ArI(OAc)₂ is described. The use of commercially available sodium hypochlorite pentahydrate (NaClO·5H₂O) enabled safe, rapid, and inexpensive oxidation of iodoarenes with electron-withdrawing and -donating substituents. The method allows tandem divergent access to synthetically useful organo-λ³-iodanes such as hydroxyl(tosyloxy)iodobenzene, iodosylbenzene, iodonium ylide, etc.

Towards an Asymmetric Organocatalytic α-Azidation of β-Ketoesters

Detailed investigations concerning the organocatalytic (asymmetric) α-azidation of prochiral β-ketoesters were carried out. It was shown that the racemic version of such a reaction can either be carried out under oxidative conditions using TMSN₃ as the azide-source with quaternary ammonium iodides as the catalysts, or by using hypervalent iodine-based electrophilic azide-transfer reagents with different organocatalysts. In addition, the latter strategy could also be carried out with modest enantioselectivities when using simple cinchona alkaloid catalysts, albeit with relatively low yields.

α-N-Heteroarylation and α-Azidation of Ketones via Enolonium Species

Enolonium species, resulting from the umpolung of ketone enolates by Koser's hypervalent iodine reagents activated by boron trifluoride, react with a variety of nitrogen heterocycles to form α-aminated ketones. The reactions are mild and complete in 4-5 h. Additionally, α-azidation of the enolonium species takes place using trimethylsilyl azide as a convenient source of azide nucleophile.

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.

Synthesis of geminal bis- and tristriazoles: exploration of unconventional azide chemistry

A range of geminal bis- and tristriazoles are presented.

Various difunctionalizations of acrylamide: an efficient approach to synthesize oxindoles

In this review, we summarize the advancement and applications in the difunctionalization of acrylamide to synthesize oxindoles based on the mechanism.

Iron(iii) chloride hexahydrate-promoted selective hydroxylation and chlorination of benzyl ketone derivatives for the construction of hetero-quaternary scaffolds

A tunable α-hydroxylation/α-chlorination of benzylketone derivatives for the construction of hetero-quaternary units has been developed by iron(iii) chloride hexahydrate-mediated selective transformations.

Towards an asymmetric organocatalytic α-cyanation of β-ketoesters

This communication describes the first proof of concept for an asymmetric α-cyanation of β-ketoesters using a hypervalent iodine-based electrophilic cyanide-transfer reagent. A series of different organocatalysts has been investigated and it was found that the use of naturally occurring Cinchona alkaloids allows obtaining the target products in good yields and with moderate enantioselectivities up to er = 76:24 under operationally simple conditions.

A new tool to guide halofunctionalization reactions: the halenium affinity (HalA) scale

We introduce a previously unexplored parameter-halenium affinity (HalA)- as a quantitative descriptor of the bond strengths of various functional groups to halenium ions. The HalA scale ranks potential halenium ion acceptors based on their ability to stabilize a "free halenium ion". Alkenes in particular but other Lewis bases as well, such as amines, amides, carbonyls, and ether oxygen atoms, etc., have been classified on the HalA scale. This indirect approach enables a rapid and straightforward prediction of chemoselectivity for systems involved in halofunctionalization reactions that have multiple nucleophilic sites. The influences of subtle electronic and steric variations, as well as the less predictable anchimeric and stereoelectronic effects, are intrinsically accounted for by HalA computations, providing quantitative assessments beyond simple "chemical intuition". This combined theoretical-experimental approach offers an expeditious means of predicting and identifying unprecedented reactions.

Synthesis of β-ketoesters from renewable resources and Meldrum's acid

β-Ketoesters are valuable building blocks for the synthesis of compounds with different biological activities.

Iodoarene-catalyzed fluorination and aminofluorination by an Ar-I/HF·pyridine/mCPBA system

We have developed the iodoarene-catalyzed fluorination of carbonyl compounds and intramolecular aminofluorination of ω-amino-alkenes using HF/mCPBA.