Organic syntheses using indium-mediated and catalyzed reactions in aqueous media

Combined Lewis Acid Catalyzed Diastereoselective Halogenative Cascade Annulation of Enone-Tethered Cyclohexadienones

The cascade difunctionalization of α,β-unsaturated carbonyls by nucleophilic halogenation followed by enolate trapping with other electrophiles is highly challenging in synthetic organic chemistry. Herein, we report a chemo- and diastereoselective cascade annulation of enone-tethered cyclohexadienones by using an unconventional combined Lewis acid catalyzed halogenation reaction in the presence of an In(III)-catalyst and trimethylsilyl halide. The reaction provides highly functionalized bicyclic enones with four contiguous stereocenters.

Synthesis and Characterization of Tetrakis(pentafluoroethyl)indate Salts

In the rising field of organoindium chemistry little is known about the perfluoroorganyl-substituted indium compounds. The increasing use of indium reagents is explained by their high stability and tolerance towards water and functional groups. Here we report on the synthesis of the novel tetrakis(pentafluoroethyl)indate, [In(C₂ F₅ )₄ ]^- , and its characterization in salts with the cations [Li(thf)₃ ]⁺ , Cs⁺ , [PPh₄ ]⁺ and [H₁₄ O₆ ]²⁺ (thf=tetrahydrofuran). To the best of our knowledge, these salts constitute the first perfluoroalkylindates and, in general, the first isolated perfluoroalkylindium compounds which are fully characterized by NMR spectroscopy, mass spectrometry, elemental analysis and X-ray diffraction analysis.

Comparison of Imine- and Phosphinimine-Supported Indium Complexes: Tuning the Reactivity for the Sequential and Simultaneous Copolymerization of Lactide and ε-Caprolactone

Imine- and phosphinimine-supported indium complexes were used as catalysts in the polymerization of racemic lactide and ε-caprolactone as well as their copolymerization by the sequential and simultaneous addition of monomers. Tuning the electronics and sterics of the indium centers by either (i) changing the nature of the nitrogen donors and (ii) coordinating a hemilabile side group had a significant effect on the reactivity of the complexes, their stability, and their control in the synthesis of block copolymers. Specifically, the imine-supported complex (5) showed the highest activity in the homo- and copolymerization of the cyclic esters, in contrast to the phosphinimine-supported complex (7), which was significantly slower and less stable. The presence of morpholine and thiomorpholine hemilabile side groups either reduced the activity or prevented the formation of alkoxide complexes.

Carbon–carbon bond formation and green chemistry: one dream and 30 years hence

Carbon–carbon bond formation is the core of organic synthesis, in which organometallic reagents play the key role in the forms of 1,2-nucleophilic additions, conjugate additions, and transition-metal catalyzed cross-couplings. These reactions have enabled the production of a wide range of organic molecules in our society. Despite the enormous power of organometallic reagents in chemical synthesis, they have inherent drawbacks in the eyes of future sustainability. This account summarizes our efforts over the past three decades on the exploration of new scientific means to overcome the drawbacks and limitations of these classical organometallic reactions.

Indium-Catalyzed Cycloisomerization of 1,6-Cyclohexenylalkynes

Efficient four- and five-step routes to access functionalized bicyclo[3.2.1]oct-2-ene and bicyclo[3.3.1]nonadiene via indium-mediated cycloisomerization of 1,6-enynes has been developed. This atom-economical catalytic process was optimized and relied on the efficiency of InCl3 leading to the preparation of functionalized bicyclic adducts in up to 99% isolated yield. The cyclization occurred on two different processes (5-exo versus 6-endo pathway) and were influenced by the substitution of the alkynyl moiety. The exo process was favored for non-substituted alkynes whereas the endo pathway was generally observed for substituted alkynes. Then, the presence of electron-withdrawing groups on the aryl substituted alkyne increased the ratio of the exo isomer. DFT calculations were performed on stability of intermediates and corroborated the intervention of InCl3.

A cooperative zinc/catalytic indium system for the stereoselective sequential synthesis of (E)-1,3-dienes from carbonyl compounds

A novel cooperative system based on zinc/catalytic indium for the stereoselective synthesis of highly functionalized (E)-1,3-dienes from aldehydes and ketones has been developed.

Catalyst- and reagent-free 1,6-hydrophosphonylation of p-quinone methides: a practical approach for the synthesis of diarylmethyl phosphine oxides

We developed a catalyst-, reagent-, and additive-free protocol with 100% atom economy for the synthesis of diarylmethyl phosphine oxides via 1,6-hydrophosphonylation of p-quinone methides using water as a green solvent. The reaction showed broad scope with excellent functional group tolerance. The practicability of this method was demonstrated by carrying out the reaction on the gram scale whereby product was obtained in high yield by the filtration technique avoiding chromatographic purification.

Indium tribromide/[bmim]PF6: A novel and recyclable catalytic system for the deprotection of 1,1-diacetates

A mild and highly efficient method has been developed for the deprotection of 1,1-diacetates using a catalytic amount of indium tribromide immobilised in 1-butyl-3-methylimidazolium hexafluorophosphate as an ionic liquid. This affords the corresponding the parent aldehydes in excellent yields. The recovered ionic liquid containing catalyst has been recycled in three subsequent runs.

InCl3·4H2O/TMSCl-Catalysed Aldol Reaction of Aromatic Aldehydes with Cycloalkanones in Ionic Liquid Medium

An efficient and practical preparation of α,α′-bis(substituted benzylidene) cycloalkanone derivatives from cycloalkanones and aromatic aldehydes promoted by InCl3•4H2O/TMSCl in ionic liquid ([bmim][BF4]) is described.

Organic reactions in aqueous media: I2-in-water-catalysed rapid and chemoselective oxathioacetalisation of aldehydes under mild conditions

I2 in water is found to be an efficient catalyst for the chemoselective protection of both aliphatic and aromatic aldehydes as 1,3-oxathioacetals under mild conditions. Fast reactions and excellent yields of pure products using an inexpensive and easily available catalyst and solvent are important features of this method.

Indium-Mediated Barbier allylations of Hydroxyanthraquinones: An Expedient synthesis of Novel 10-Alkenyl-10-Hydroxy-9(10H)-Anthracenones

Indium-mediated allylations of 1,8-dihydroxy-9,10-anthraquinone with allyl, cinnamyl and crotonyl bromides/ chlorides and 1,4- and 1,5- dihydroxy derivatives with allyl bromide in THF–MeOH–H2O gave the respective 10-alkenyl-10-hydroxy-9(10H)-anthracenones in excellent yields.

Gallium Mediated Barbier Reactions of 1,2-diones: A Facile Synthesis of α-hydroxy ketones

Gallium mediated allylation and cinnamylation reactions of 1,2-diones in presence of LiBr and KI afforded α-hydroxycarbonyl compounds in moderate to good yields.

Reactions in Water - A Greener Approach Using Ruthenium Catalysts

Reactions using transition metals as catalysts have emerged as an efficient method in the recent times. However, the selection of solvent plays a crucial role in this regard. Several solvents used traditionally suffer majorly with problems of toxicity; high boiling point etc. leading to drastic reaction conditions. Water being a non-toxic, non-inflammable and environmentally benign can replace the hazardous organic solvents in laboratory as well as industry. Maintaining a minimum catalyst loading percentage we can advantageously avail high levels of selectivity. Water was found to be a good solvent medium for several metal catalysed reactions. An intramolecular deprotonation mechanism is followed by the ruthenium (II) catalysts in water; thereby, facilitating the catalytic action of the metal. These studies can help the industrial chemists to utilize water as a solvent for their reactions towards improvement of their waste management procedure. This review mainly focuses on the several recent developments in the above direction.

A Simple and Convenient Synthesis of Unlabeled and 13C-Labeled 3-(3-Hydroxyphenyl)-3-Hydroxypropionic Acid and Its Quantification in Human Urine Samples

An improved method to synthesize the highly abundant and biomedically important urinary metabolite 3-(3-hydroxyphenyl)-3-hydroxypropionic acid (HPHPA) is reported. The modified protocol is based on an indium-mediated sonochemical Reformatsky reaction. The synthesis is a simple two-step route as opposed to a complex four-step route previously reported in the literature that requires specialized equipment, flammable materials, and high-pressure reaction vessels. The described procedure also provides an expedient route to prepare a 13C isotopically labeled HPHPA that can be used as a standard for quantitative LC-MS analysis. This report also illustrates how the synthesized metabolite standard was used to detect and accurately quantify its presence in human urine samples using both NMR and LC-MS techniques.

An efficient protocol for the synthesis of highly sensitive indole imines utilizing green chemistry: optimization of reaction conditions

Novel and highly sensitive indole-based imines have been synthesized. Their synthesis has been compared employing a variety of protocols. Ultimately, a convenient, economical and high yielding set of conditions employing green chemistry have been designed for their synthesis.

From Conventional Lewis Acids to Heterogeneous Montmorillonite K10: Eco-Friendly Plant-Based Catalysts Used as Green Lewis Acids

The concept of green chemistry began in the USA in the 1990s. Since the publication of the 12 principles of this concept, many reactions in organic chemistry have been developed, and chemical products have been synthesized under environmentally friendly conditions. Lewis acid mediated synthetic transformations are by far the most numerous and best studied. However, the use of certain Lewis acids may cause risks to environmental and human health. This Review discusses the evolution of Lewis acid catalyzed reactions from a homogeneous liquid phase to the solid phase to yield the expected organic molecules under green, safe conditions. In particular, recent developments and applications of biosourced catalysts from plants are highlighted.

In(III)-TMSBr-Catalyzed Cascade Reaction of Diarylalkynes with Acrylates for the Synthesis of Aryldihydronaphthalene Derivatives

A combined Lewis acid system comprising of two or more Lewis acids occasionally exhibits augmented catalytic activity in organic transformations which are otherwise unrealizable by either of the components exclusively. On the other hand, the efficient construction of multiple new C-C bonds and polycyclic structures in minimal steps remains a subject of great interest in both academia and industry. Herein we report an efficient method to assemble aryldihydronaphthalene derivatives via a cascade reaction of diarylalkynes with acrylates under the catalysis of a combined Lewis acid derived from In(III) salt and TMSBr.

Direct conjugate additions using aryl and alkyl organic halides in air and water

The direct aryl-conjugate addition to electron-deficient alkenes without prior stoichiometric formation of organometallic reagents in water catalyzed by copper represents an important but unresolved challenge.

Lewis Acid-Catalyzed Selective [2 + 2]-Cycloaddition and Dearomatizing Cascade Reaction of Aryl Alkynes with Acrylates

Combined Lewis acid, consisting of two or more Lewis acids, sometimes shows unique catalytic ability, and it may promote reactions which could not be catalyzed by any of the Lewis acids solely. On the other hand, the development of efficient methods for the facile synthesis of cyclobutenes and densely functionalized decalins is an attractive target for synthetic chemists due to their versatile synthetic utilities and widespread occurrence in natural products. Herein, we wish to report an efficient method for the assembly of cyclobutenes and densely functionalized decalin skeletons through In(tfacac)₃-TMSBr catalyzed selective [2 + 2]-cycloaddition and dearomatizing cascade reaction of aryl alkynes with acrylates with high chemo- and stereoselectivity. The obtained cyclobutene could be easily converted into cyclobutane as well as synthetically useful 1,4- and 1,5-diketones with high chemo- and stereoselectivity. On the basis of mechanistic studies, plausible reaction mechanisms were proposed for both the [2 + 2]-cycloaddition and the dearomatizing cascade reaction. Finally, the computational studies of reaction mechanisms were conducted, and the results suggest that the combined Lewis acid could efficiently promote both reactions.

Indium-Mediated Stereoselective Allylation

Stereoselective indium-mediated organic reactions have enjoyed tremendous growth in the last 25 years. This is in part due to the insensitivity of allylindium to moisture, affording facile and practical reaction conditions coupled with outstanding functional group tolerance and minimal side reactions. Despite the plethora of articles about allylindium, there is much yet to be discovered and exploited for efficient and sustainable synthesis. In this Account, we describe indium-mediated synthetic methods for the preparation of chiral amines with the aim to present a balance of practical method development, novel asymmetric chemistry, and mechanistic understanding that impact multiple chemical and materials science disciplines. In 2005, we demonstrated the indium-mediated allylation of chiral hydrazones with complete diastereoselectivity (>99:1) and quantitative yields. Further, we revealed the first example of enantioselective indium-mediated allylation of hydrazones using catalytic (R)-3,3'-bis(trifluoromethyl)-BINOL ligands to afford homoallylic amines with high enantioselectivity. The use of enantiopure perfluoroalkylsulfonate BINOLs greatly improved the indium-mediated allylation of N-acylhydrazones with exquisite enantiocontrol (99% yield, 99% ee). This laboratory has also investigated indium-mediated asymmetric intramolecular cyclization in the presence of amino acid additives to deliver biologically relevant chromanes with excellent diastereoselectivity (dr >99:1). The effect of amino acid additives (N-Boc-glycine) was further investigated during the indium-mediated allylation of isatins with allyl bromide to yield homoallylic alcohols in excellent yields in a short time with a wide range of functional group tolerance. Critical mechanistic insight was gained, and evidence suggests that the additive plays two roles: (1) to increase the rate of formation of allylindium from allyl bromide and In(0) and (2) to increase the nucleophilicity of the allylindium reagent, probably through disruption of aggregates and coordination to the metal. We recently reported the palladium-catalyzed umpolung allylation of hydrazones with allyl acetates in the presence of indium(I) iodide (InI) with excellent diastereoselectivity (up to 99:1). The conversion was found to be inversely proportional to the phosphine concentration, providing insight into the mechanism of the critical redox transmetalation process that has implications for other Pd-catalyzed umpolung-type allylation processes. A detailed overview of the work in our lab is presented with the intention of stimulating further research interest in organoindium chemistry and its application in organic synthesis.

Indium-catalyzed C(sp3)–H functionalization of 2-methylazaarenes through direct benzylic addition to trifluoromethyl ketones

The application of InCl₃ for the catalytic C(sp³)–H functionalization of 2-methylazaarenes leading to trifluoromethylated alcohols in up to 99% yield.