Current Organocatalysis (v.4, #1)

Meet Our Editorial Board Member by Georgiy B. Shul'pin (1-1).

Background: Over the past decade, catalysis by ionic liquids (ILs), has gained much attention, due to its variety in catalytic reactions that have been successfully carried out in such clean media for green chemistry, especially in synthetic and catalytic transformations. Catalysis in ILs is one of the most promising greener reactions in catalytic science. ILs, have several advantages, that they are used as alternative solvents in the progress of catalytic reactions as compared to traditional volatile organic solvents. ILs have one of the most important advantages that they have lower vapor pressure which is favorable for developing greener catalytic technologies. For this particular cause (low volatility) ILs are called as green solvents.
Methods: Recently, the development of chiral ionic liquids and their applications in asymmetric synthesis has attracted much attention as these reactions have widespread applications in the synthesis of chiral drugs and pharmaceutical industries.
Results: Asymmetric induction is mainly achieved by the use of chiral substrates or reagents, chiral catalysts or enzymes. There are also numbers of structurally modified ILs that have been synthesized at room temperature. This review focuses on imidazolium ionic liquids that possess chirality either in imidazolium or in anion moiety.
Conclusions: The aim of this review is to highlight the recent breakthrough of Chiral ILs in chirality transfer or chiral recognition when used as solvent or co-solvent: the case of task specific ionic liquids is beyond the scope of this review. In the first part, the synthesis of CILs will be presented while the second part will be devoted to their use in the field of asymmetric synthesis as well as various pharmaceutical industries.

Since 1990s, the application of organo-iodine reagents as oxidant in organic synthesis went through explosive progress. In early times, most of organo-iodine reagents were used as stoichiometric terminal or co-oxidants in oxidative reactions, which inevitably led a lower atom coefficient of utilization and environmental issues. In this regard, it is very urgent to develop varies of efficient approaches of the catalytic utilization of organo-iodine reagents in organic synthesis. Recently, more and more iodine compounds were used as organo-catalysts for many kinds of reactions, which were revolutionary progress for iodine chemistry, and could also meet the need of green chemistry. In this review, we presented an overview of catalytic utilization of active iodine reagents as organo-catalysts in organic synthesis and also some successful examples for asymmetric catalysis. We focused on the recent synthetic strategies, applications of organo-iodine reagents and its mechanism as organo-catalysts, and finally gave a perspective of future development.

Organic Polymeric Resins Embedded with Pd NPs: Newly Designed, Efficient and Chemoselective Catalyst for Reduction of Nitrobenzenes by Basudeb Basu, Susmita Paul, Samir Kundu, Emil Byström, Knut Irgum, Fredrik Almqvist (48-61).
Background: Organic polymer supported palladium nanoparticles (NPs) are important for use as heterogeneous catalyst in various organic reactions. This works describes Pd Nps immobilized on to polystyrene-based ion-exchange resin surface for use as catalyst in the reduction of nitrobenzenes. The heterogeneous catalyst was found useful for hydrogenation of nitro group under both catalytic transfer hydrogenation (CTH) as well as by using molecular hydrogen (H2).
Methods: The catalyst was prepared from Amberlite IRA 900 Cl after rinsing with formic acid (10%) and subsequent treatment with Na2PdCl4 in DMF. The resulting Pd Nps immobilized resins was designated as VersaCat Pd and used for CTH of nitrobenzenes in the presence of H-donors (sodium formate, formic acid, hydrazine hydrate) and also for hydrogenation with H2 gas. The catalyst was characterized by FT-IR, MAS-NMR, SEM, TEM and XPS and surface morphologies were studied before and after the reaction.
Results: Hydrogenations of nitrobenzenes under CTH using different H-source and direct use of H2 gas were achieved successfully with good to excellent yields. Reactions were performed under mild conditions and high degree of chemoselectivity was also observed. The catalyst was recyclable, used for six consecutive runs with appreciable conversions and showed higher activity (> 3 times) in terms of metalcontent than commercially available Pd/C (10%) in the hydrogenation of nitrobenzenes using H2 gas. The TEM images showed that Pd Nps are evenly distributed with size 50-200 mm on polymeric matrices and there was no significant changes observed after the first catalytic run. However, considerable rupture of the polymeric surface occurred after six runs, as seen from SEM studies.
Conclusion: The present study establishes high catalytic efficiency and chemoselectivity of the newly developed organic polystyrene-based resin-soaked Pd NPs (VersaCat Pd) in the reduction of nitrobenzenes. Both CTH and hydrogenation using H2 gas were successfully done. Interestingly, hydrazine hydrate offered excellent control over chemoselectivity under CTH conditions and allowed clean conversion from nitro to amine, while keeping a chloro substitutent unaffected. Hydrogenation using molecular H2 gave maximum TOF. Easy preparation, high efficacy, TOF, chemoselectivity, and versatile applications are notable features for this heterogeneous palladium catalyst (VersaCat Pd). These features are often required in chemical industries.

Oxidation of Alcohols by Hydrogen Peroxide Catalyzed by Trinuclear Copper(II) Complex [Cu3(slmh)(µ-Cl)2(CH3OH)3].0.5CH3OH derived from Disalicylaldehyde Malonoyldihydrazone by Sunshine D. Kurbah, Arvind Kumar, Sankey Shangpung, Mrityunjaya Asthana, Ibanphylla Syiemlieh, Ram A. Lal (62-68).
Background: The oxidation of alcohols to afford carbonyl compounds is a key transformation in organic chemistry. Significant development has occurred in the recent years, in catalytic oxidation of alcohols by aerial oxygen. However, the alcohol oxidation mediated by H2O2 is quite meagre. From economic and environmental point of views, the oxidation of alcohols mediated by H2O2 is quite attractive in particular.
Methods: Various alcohols Cu3(slmh)(µ-Cl)2(CH3OH)3].0.5CH3OH, ligand, H2O2, CDCl3, Tetramethylsilane were used for oxidation of alcohols to carbonyl compounds. For analysis, IR, 1H NMR, and 13C NMR were utilized.
Results: Taking benzyl alcohol as a model compound, first reaction conditions were optimized. The combination of catalyst (0.04 mmol, 0.032 mg), 15% H2O2 (8.83 mmol, 2 mL) at 70°C under solvent free condition was found to be the most appropriate condition for the oxidation of alcohols. The efficiency of the catalyst was tested by oxidizing several aromatic ring substituted benzyllic, aliphatic and allylic alcohols by H2O2. We efficiently carried out oxidation of nineteen alcohols. The benzyl alcohols bearing electron withdrawing groups gave excellent yield of the corresponding carbonyl compounds whereas those bearing electron donating substituent gave slightly lower conversions. The heteroaroyl alcohols also gave excellent yield. The hydroxy group was oxidized selectively to aldehyde in cinnamyl alcohol keeping double bond intact. Secondary alcohols such as cyclohexane and 1-phenylethanol were negligibly oxidized. The aliphatic alcohols gave much lower yield as compared to benzyllic and allylic alcohols.
Conclusion: The benzyllic, aliphatic and allylic alcohols were effectively oxidized to aldehydes by hydrogen peroxide using catalytic amount of Cu3(slmh)(µ-Cl)2(CH3OH)3].0.5CH3OH. The process is simple and mild, the catalyst can be recycled to get improved catalytic activity.

Efficient and Green Synthetic Protocol for the Synthesis of Structurally Diverse Spiroheterocycles using GAAS as Catalytic Solvent by Sarita Khandelwal, Anshu Rajawat, Yogesh Kumar Tailor, Anju Kulhari, Mahendra Kumar (69-74).
Background: The development of novel synthetic methods for the synthesis of structurally diverse drug-like molecules with environmentally friendly solvents and catalysts is significant in the development of drug discovery research. The synthesis of fused heterocycles has attracted considerable interest because the fusion of biologically active heterocyclic systems has proved to be an attractive and useful approach for designing potential drugs with a wide spectrum of pharmacological activities. Multicomponent reactions with their highly convergent characteristics offer an opportunity to provide druglike small molecules with structural diversity and molecular complexity. The present synthetic protocol involves the tandem reaction of hydrazine hydrate, 3-aminocrotononitrile, isatins and carbonyl compound using GAAS as environmentally benign and sustainable catalytic solvent.
Method: spirooxindoles spiroannulated with indenopyrazolopyridine, chromenopyrazolopyridine, and pyranopyrazolopyridine have been synthesized by multicomponent reaction of hydrazine hydrate, 3- aminocrotononitrile, cyclic 1,3-diketones, and substituted isatines in the presence of gluconic acid aqueous solution (GAAS, 50 wt%) as catalytic solvent.
Results: we have presented diversity oriented efficient and environmentally benign synthetic protocol for the synthesis of structurally diverse spiroannulated pyrazolo[3,4-b]pyridines using gluconic acid aqueous solution (GAAS, 50%, wt%) as an inexpensive and eco-friendly bio-based catalytic solvent.
Conclusion: The operational simplicity with mild reaction conditions, shorter reaction times, excellent product yields and environmentally benign reaction conditions with reusability of catalytic solvent render the present protocol both attractive and economically viable for the synthesis of medicinally privileged spiroannulated heterocycles. We believe that the present work will contribute considerably not only to the chemical research, but also to the medicinal research.

Background: The palladium-catalyzed couplings of alkenes with aryl halides is considered as one of the most important methods for carbon-carbon bond formation and have been utilized in the areas of natural products, high performance materials, bioactive compounds, new drugs and many industrially useful chemicals. Although the homogeneous palladium catalysts offer several advantages concerning higher selectivity and yields, better tuning of chemoselectivity and high efficiency but commercializing most of homogeneous has not been possible because of recycling problem of the catalyst from the mixture of reaction. Therefore, for resolving this problem, immobilization of homogeneous Pd complexes via grafting to solid supports such as activated carbon, zeolites, silica or modified silica, polymers, nanoparticles, and magnetic core shells have been subject of great challenges.
Methods: Fe3O4 nanoparticles was coated by silica gel and then decorated by Schiff base Pd complex to provide Fe3O4@SiO2/Schiff base/Pd(II) nanoparticles. After optimization of reaction parameters, Heck- Mizoroki coupling reaction of aryl halides with olefins was studied.
Results: The magnetic Schiff base complex of Pd, as a phosphine free nanocatalyst, catalyzed efficiently Heck-Mizoroki carbon-carbon coupling reaction between aryl halides and alkenes and provided the desired products in high yields. The magnetic Pd complex was easily removed from the reaction mixture and reused for eight runs. Conclusion: A new efficient, simple and cost effective protocol was introduced for carbon-carbon bond formation via Heck-Mizoroki coupling reaction of aryl halides with olefins in high to excellent yields in short reaction times. These valuable advantages were achieved because of employing Fe3O4@SiO2/Schiff base/Pd(II) complex as a dispersible, phosphine free ligand, highly active, magnetically recoverable and reusable several times.