Metal-free oxidative cyclization of urea-tethered alkenes with hypervalent iodine

A metal-free oxidative cyclization of ureas onto unactivated alkenes using iodosylbenzene and an acid promoter is described. The products isolated are predominantly bicyclic isoureas resulting from an intramolecular oxyamination reaction. The acid type and urea substitution have a strong effect on the product formed. A variety of substrates form the isourea with high diastereoselectivity via syn addition including di- and trisubstituted alkenes. Hydrolysis of the isourea gives access to new diastereomerically pure prolinol derivatives.     

Substituent effects in addition of iodine thiocyanate to alkenes

The plots of logarithms of relative rates of ISCN addition to alkenes versus alkene IPs and versus alkene HOMO energies reveal that the alkene relative reactivity depends upon both electronic and steric effects of the substituents. Steric effects are related not only to the degree of substitution on the CC bond but also to the relative position, size, and branching of alkyl substituents.     

Iodofluorination of alkenes and alkynes promoted by iodine and 4-iodotoluene difluoride

It was found that a mixture of molecular iodine and 4-iodotoluene difluoride are useful to generate in situ the couple ‘IF’ that was able to add in a Markovnikov fashion and with prevalent anti-stereoselectivity to various alkenes and alkynes.     

Mechanism of cis/trans equilibration of alkenes via iodine catalysis

Iodine is commonly used to speed the equilibration of Wittig cis/trans alkene products. This study uses computational chemistry to study the catalyzed isomerization mechanism in detail for seven different examples of 1,2-disubstituted alkenes. We find that the iodo intermediates of the conventional three-step reaction path are weakly stable, bound by less than 7 kJ mol(-1) in five cases and nonexistent in the other two. These variations in relative stability appear to be closely related to the degree of conjugation interruption in the alkene upon attachment of iodine. The rate-determining reaction barrier always occurs in the middle step, the internal rotation of the iodo intermediate, and the variations in the barrier heights are dictated by varying levels of steric hindrance in the seven cases. Regiospecificity of I-atom addition and noticeable hyperconjugative effects are discussed. Comparisons between various theoretical approximations are performed to demonstrate the great difficulty in obtaining accurate results for iodine-atom bond-forming and bond-breaking energies.     

A three-component reaction between alkenes, secondary phosphanes, and elemental selenium: a novel, efficient, atom-economic synthesis of diselenophosphinic esters

A novel, convenient, atom-economic approach toward the synthesis of diselenophosphinic esters has been developed via the three-component reaction between aryl- or hetarylalkenes secondary phosphanes, and elemental selenium. The reaction proceeds without a catalyst (85 °C, 3 h, 1,4-dioxane) to afford the target compounds in good to high yields.     

Oxidative rearrangement of alkenes using in situ generated hypervalent iodine(III)

A novel protocol for the oxidative rearrangement of alkenes using in situ generated hypervalent iodine(III) was developed. This approach uses inexpensive, readily available, and stable chemicals (PhI, mCPBA, and TsOH) giving rearrangement products in yields comparable to those obtained using the more expensive commercially available [hydroxy(tosyloxy)iodo]benzene [HTIB or Koser’s reagent]. Additionally, an alternative protocol for the synthesis of 1-methyl-2-tetralone through the one-step epoxidation/rearrangement of 4-methyl-1,2-dihydronaphthalene using mCPBA and TsOH was developed.     

Regio- and stereoselective co-iodination of olefins using NH4I and Oxone

A simple, efficient, and environmentally benign protocol for the synthesis of vicinal iodohydrins and iodoesters from olefins using NH₄I and Oxone in CH₃CN/H₂O (1:1) and dimethylformamide (DMF) / dimethylacetamide (DMA), respectively, without employing a catalyst at room temperature is described. Regio- and stereoselective iodohydroxylation and iodoesterification of various olefins with anti fashion, following Markonikov’s rule, was achieved and the corresponding products were obtained in good to excellent yields. In addition, 1,2-disubstituted olefins afforded excellent diastereoselectivity.     

Ruthenium-catalyzed reactions--a treasure trove of atom-economic transformations

The demand for new chemicals spanning the fields of health care to materials science combined with the pressure to produce these substances in an environmentally benign fashion pose great challenges to the synthetic chemical community. The maximization of synthetic efficiency by the conversion of simple building blocks into complex targets remains a fundamental goal. In this context, ruthenium complexes catalyze a number of non-metathesis conversions and allow the rapid assembly of complex molecules with high selectivity and atom economy. These complexes often exhibit unusual reactivity. Careful consideration of the mechanistic underpinnings of the transformations can lead to the design of new reactions and the discovery of new reactivity.     

New procedure for the preparation of highly sterically hindered alkenes using a hypervalent iodine reagent

New methodology is described to construct the olefinic bond in overcrowded alkenes using a hypervalent iodine reagent, and applied in the synthesis of molecular motors.     

Metallic samarium and iodine promoted facile and efficient syntheses of trisubstituted alkenes from the acetates of Baylis-Hillman adducts

Promoted by samarium metal in the presence of a catalytic amount of iodine, the Baylis-Hillman adducts underwent reductive elimination to form (E)-methylcinnamic ester derivatives. When the iodine was used in 1:1 ratio with metallic samarium, stereospecific syntheses of allylic iodide derivatives, (2Z)-2-(iodomethyl)alk-2-enoates, were achieved. Thus, this gives a new approach to the selective construction of stereo-defined trisubstituted alkenes with the simple Sm/I₂ system.     

Aerobic intramolecular aminothiocyanation of unactivated alkenes promoted by in situ generated iodine thiocyanate

Aerobic intramolecular aminothiocyanation of unactivated alkenes has been developed by in situ generated iodine thiocyanate under open-flask conditions. This protocol provides a concise and efficient method for synthesizing SCN-containing pyrrolidine, piperidine and indoline derivatives with isolated yields of up to 87%. Furthermore, mixing iodine and sodium thiocyanate with oxygen afforded iodine thiocyanate (ISCN) and dithiocyanatoiodate [I(SCN)₂]^- which were testified by liquid chromatography mass spectrometry. A mechanistic investigation indicates that iodonium ion and sulfonium ion intermediates might be involved in this transformation.     

m-Iodosylbenzoic acid, a tagged hypervalent iodine reagent for the iodo-functionalization of alkenes and alkynes

An efficient and facile method for the iodo-functionalization of alkenes 5 and alkynes 6 by using recyclable m-iodosylbenzoic acid (2) was developed. The final products can be easily isolated without any chromatographic purification by simple treatment of the crude mixture with an anionic exchange resin. Unreacted m-iodosylbenzoic acid and reduced m-iodobenzoic acid are effectively recovered from the resin by acidification with hydrochloric acid.     

An atom-economic synthesis of nitrogen heterocycles from alkynes

A robust route to 2,4-disubstituted pyrrole heterocycles relying upon a cascade reaction is reported. The reaction benefits from operational simplicity: it is air and moisture tolerant and is performed at ambient temperature. Control over the reaction conditions provides ready access to isopyrroles, 2,3,4-trisubstituted pyrroles, and 3-substituted pyrollidin-2-ones.     

Catalytic synthesis of sulfur and phosphorus compounds via atom-economic reactions

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A facile and highly atom-economic approach to biaryl-containing medium-ring bislactones

Starting from readily available phenanthrenequinone and alkenes, biaryl containing medium-ring bislactones could be easily prepared through sequential photocycloaddition-photooxidation reactions with good yields and diastereoselectivity.