High‐Pressure 31P{1H} NMR Studies of RhH(CO)(TPPTS)3 in the Presence of Methylated Cyclodextrins: New Light on Rhodium‐Catalyzed Hydroformylation Reaction Assisted by Cyclodextrins

The effect of methylated cyclodextrins on the RhH(CO)(TPPTS)₃ complex in hydroformylation conditions [50 atm of CO/H₂ (1/1) and 80 °C] has been investigated by high‐pressure ³¹P{¹H} NMR spectroscopy. In the presence of methylated β‐cyclodextrin, the equilibria between the rhodium species lie in favor of phosphine low‐coordinated rhodium species. The formation of a stable inclusion complex between this cyclodextrin and the trisulfonated triphenylphosphine ligand (TPPTS) was found to be the key to understanding the displacement of the equilibria. Indeed, the methylated α‐cyclodextrin which does not interact with the TPPTS and the methylated γ‐cyclodextrin which can weakly bind to the TPPTS have no and a very low effect on the equilibria, respectively. These results explain for the first time why a decrease in the normal to branched aldehydes ratio is always observed when cyclodextrins are used as mass‐transfer agents in aqueous biphasic hydroformylation processes.     

Biphasic Aqueous Organometallic Catalysis Promoted by Cyclodextrins: How to Design the Water‐Soluble Phenylphosphane to Avoid Interaction with Cyclodextrin

The ability of cyclodextrin to interact with meta‐trisulfonated triphenylphosphane derivatives bearing one or two methyl (or methoxy) groups on the aromatic ring has been investigated by NMR and UV‐vis spectroscopy. In the case of native β‐cyclodextrin (β‐CD), the presence of one methyl or methoxy group in the ortho‐position on each aromatic ring is necessary to hamper the formation of an inclusion complex between the β‐CD and meta‐trisulfonated triphenylphosphane derivatives. In the case of methylated β‐CD, the formation of an inclusion complex is only observed when the meta‐trisulfonated triphenylphosphane contains a methyl group in the para‐position. The poor affinity of methylated β‐CD towards modified trisulfonated triphenylphosphanes was attributed to the steric hindrance generated by the methyl groups on the CD secondary face. The absence or presence of an interaction between phosphanes and methylated β‐CD was also confirmed by catalytic experiments. Thus, the phosphanes that do not interact with the methylated CD were the most efficient mass‐transfer promoters in an aqueous biphasic palladium‐catalyzed Tsuji–Trost reaction.     

n‐butane carbonylation to n‐pentanal using a cascade reaction of dehydrogenation and SILP‐catalyzed hydroformylation

A novel gas‐phase process has been developed that allows direct two‐step conversion of butane into pentanals with high activity and selectivity. The process consists of alkane dehydrogenation over a heterogeneous Cr/Al₂O₃ catalyst followed by direct gas‐phase hydroformylation using advanced supported ionic liquid phase (SILP) catalysis. The latter step uses rhodium complexes modified with the diphosphite ligands biphephos (BP) and benzopinacol to convert the butane/butene mixture from the dehydrogenation step efficiently into aldehydes. The use of the BP ligand results in improved yields of linear pentanal because SILP systems with this ligand are active for both isomerization and hydroformylation. © 2014 American Institute of Chemical Engineers AIChE J, 61: 893–897, 2015     

Diastereoselective and Enantioselective Epoxidation of Acyclic β‐Trifluoromethyl‐β,β‐Disubstituted Enones by Hydrogen Peroxide with a Pentafluorinated Quinidine‐Derived Phase‐Transfer Catalyst

An efficient catalytic asymmetric epoxidation of β‐trifluoromethyl‐β,β‐disubstituted unsaturated ketones has been achieved by a pentafluorine‐substituted phase‐transfer catalyst with hydrogen peroxide (30%). Thus, the β‐trifluoromethyl‐α,β‐epoxy ketones with a quaternary carbon centre were obtained in excellent diastereoselectivities (up to 100:1 dr) and excellent enantioselectivities (up to 99.7% ee). Low catalyst loading, recycle of catalyst, environmentally benign oxidant and easy transformation of the epoxides into medicinally important trifluoromethylated intermediate make our protocol much more practical.     

Catalysis by β‐Cyclodextrin Hydrate – Synthesis of 2,2‐Disubstituted 2H‐Chromenes in Aqueous Medium

A cost‐effective, operationally simple and eco‐compatible protocol for the one‐pot synthesis of photochromic pyrans by the reaction of propargyl alcohols as well as propargyl ethers with differently substituted phenols under ambient atmosphere in aqueous medium has been developed using β‐cyclodextrin hydrate as an efficient, recyclable and stable catalyst. This is the first report where β‐cyclodextrin hydrate acted as a catalyst for an organic transformation but β‐cyclodextrin alone failed.

     

Novel lipase isolated from a Pseudomonas strain and its application in the synthesis of S(+)‐2‐O‐benzylglycerol‐1‐acetate

Isolation of a novel microbial lipase (EC 3.1.1.3) having specific catalytic activity for the synthesis of optically pure 2‐O‐benzylglycerol‐1‐acetate, the building block for the preparation of many β‐blockers, phospholipase A2 inhibitors and other biologically active compounds was the aim of this investigation. A Pseudomonas (strain G6), recently isolated from soil, produced an extracellular lipase. SDS–PAGE analysis showed that the lipase protein was a hexamer. The molecular weight of the sub‐units of the lipase protein were 10, 19, 29, 30, 47 and 53. The catalytic activity of the lipase was exploited for the synthesis of 2‐O‐benzylglycerol‐1‐acetate from 2‐O‐benzylglycerol through transesterification using vinyl acetate as acylating agent. High selectivity of the lipase towards the monoacetate product was demonstrated. A 97% enantiomeric excess (ee) of S(+)‐2‐O‐benzylglycerol‐1‐acetate was obtained when the reaction was carried out at room temperature with shaking. The lipase was highly active in anhydrous organic microenvironments and in non‐polar organic solvents with log P values above 2.5. © 2002 Society of Chemical Industry     

Novel Aqueous Phase Supramolecular Synthesis of 3‐Pyrrolylindolin‐2‐ones and Pyrrolylindeno[1,2‐b]quinoxalines

Various 3‐pyrrolylindolin‐2‐ones and pyrrolylindeno[1,2‐b]quinoxaline were synthesized for the first time in high yields in water under neutral conditions by supramolecular catalysis involving β‐cyclodextrin. The β‐cyclodextrin can be recovered and reused a number of times without any loss of activity.     

Sulfobutyl Ether‐β‐Cyclodextrins: Promising Supramolecular Carriers for Aqueous Organometallic Catalysis

The potentialities of sulfobutyl ether‐β‐CDs derivatives as supramolecular carrier in a biphasic Tsuji–Trost reaction catalyzed by a water‐soluble palladium complex of trisulfonated triphenylphosphine have been investigated. The efficiency of these cyclodextrins (CDs) strongly depends on the average molar substitution degree of cyclodextrin and the highest rate enhancements were obtained with cyclodextrins containing about 7 sulfobutyl ether groups. This result was attributed to the absence of a strong interaction between this cyclodextrin and the trisulfonated triphenylphosphine used to dissolve the catalyst in the aqueous phase and to the presence of an extended hydrophobic cavity allowing a better molecular recognition between the substrate and the cyclodextrin. This constitutes the first example of a non‐interacting β‐cyclodextrin/phosphine couple with high catalytic activities.     

Synthesis,Rhodium Complexes and Catalytic Applications of a New Water‐Soluble Triphenylphosphane‐Modified β‐Cyclodextrin

A new triphenylphosphane based on a β‐cyclodextrin skeleton (PM‐β‐CD‐OTPP) was synthesized. This ligand can be dispersed in water by using the nanoprecipitation method. Transmission electron microscopy and NMR spectroscopy showed that PM‐β‐CD‐OTPP is aggregated in water and forms a stable dispersion. Its aqueous solubility can be dramatically increased in the presence of selected water‐soluble guests by formation of inclusion complexes. Associated to a rhodium precursor, PM‐β‐CD‐OTPP is able to generate soluble rhodium species in water. In addition, NMR experiments showed that the cyclodextrin cavity remains accessible for a guest even when PM‐β‐CD‐OTPP is coordinated to rhodium. Finally, this ligand was efficient for rhodium‐catalyzed hydrogenation and hydroformylation performed in aqueous medium.     

Phase‐Transfer‐Catalyzed Olefin Isomerization/α‐Alkylation of α‐Alkynylcrotonates as a Route for 1,4‐Enynes

The phase‐transfer‐catalyzed alkylation of α‐alkynylcrotonates was developed as a means to provide 1,4‐enynes deconjugated by an all‐carbon quaternary center. Extension to the asymmetric version using the chiral phase‐transfer catalyst (S)‐ 3 provided the alkylated compounds with up to 87% ee.     

Synthesis of an Enantiocomplementary Catalyst of β‐Isocupreidine (β‐ICD) from Quinine

Compound 20 , a pseudoenantiomer of β‐isocupreidine (β‐ICD), was synthesized from quinine employing a Barton reaction of nitrosyl ester 13 and acid‐catalyzed cyclization of carbinol 18 as key steps. The Baylis–Hillman reaction of benzaldehyde, p‐nitrobenzaldehyde, and hydrocinnamaldehyde with 1,1,1,3,3,3‐hexafluoroisopropyl acrylate (HFIPA) using 20 as a chiral amine catalyst was found to give the corresponding S‐enriched adducts in high optical purity (>91% ee) in contrast to the β‐ICD‐catalyzed reaction which affords R‐enriched adducts. This result suggests that compound 20 can serve as an enantiocomplementary catalyst of β‐ICD in the asymmetric Baylis–Hillman reaction of aldehydes with HFIPA.     

Selectivity of Rhodium‐Catalyzed Hydroformylation of 1‐Octene during Batch and Semi‐Batch Reaction using Trifluoromethyl‐Substituted Ligands

The regioselectivity of catalysts generated in situ from dicarbonyl rhodium(I)(2,4‐pentanedione) and trifluoromethyl‐substituted triphenylphosphine ligands has been evaluated during the hydroformylation of 1‐octene. The influence of batch or semi‐batch operation, the solvent, and the number of trifluoromethyl substituents has been investigated. During batch operation in a supercritical carbon dioxide (CO₂)‐rich system the differential n:iso ratio increases from approximately 4 to a value of 12–16 at about 90–95 % conversion for the catalyst based on bis[3,5‐bis(trifluoromethyl)phenyl]phenylphosphine. For semi‐batch conditions using hexane a constant n:iso ratio is obtained over a broad conversion range. Batch hydroformylation in neat 1‐octene is faster than in a supercritical CO₂‐rich, one‐phase system, with a similar overall selectivity as observed in the supercritical case. The results provide further directions for the development of ligands that are especially designed for the separation of homogeneous catalysts in continuously operated hydroformylation in scCO₂.     

A water‐soluble supramolecular‐structured photoinitiator between methylated β‐cyclodextrin and 2,2‐dimethoxy‐2‐phenylacetophenone

A water‐soluble supramolecular‐structured photoinitiator (SSPI) was synthesized by supramolecular self‐assembling between methylated β‐cyclodextrin (MβCD) and hydrophobic 2,2‐dimethoxy‐2‐phenylacetophenone (DMPA). The structure of SSPI was characterized by X‐ray diffraction, FTIR, ¹H NMR, UV–vis, and fluorescence spectra. The results indicated that MβCD and DMPA had formed 1 : 1 inclusion complex in methanol solution. The binding constant (K) for the complex was 7.51 × 10²M^?1. SSPI could be dissolved in water easily and its water‐solubility was 15.3 g/100 mL. SSPI was the more efficient photoinitiator than DMPA for the photopolymerization of acrylamide (AM) in homogeneous aqueous system. The conversion for photopolymerization of trimethylolpropane triacrylate system initiated by SSPI was similar to that initiated by DMPA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of grafting β‐cyclodextrin with chitosan

Two new adsorbents [β‐cyclodextrin–chitosan (β‐CD–CTS) and β‐cyclodextrin‐6–chitosan (β‐CD‐6‐CTS)] were synthesized by the reaction of β‐cyclodextrin (β‐CD) with epoxy‐activated chitosan (CTS) and the sulfonation of the C‐6 hydroxyl group of β‐cyclodextrin with CTS, respectively. Their structures were confirmed by IR spectral analysis and X‐ray diffraction analysis, and their apparent amount of grafting was determined by ultraviolet spectroscopy. The adsorption properties of β‐CD‐CTS and β‐CD‐6‐CTS for p‐dihydroxybenzene were studied. The experimental results showed that the two new adsorbents exerted adsorption on the carefully chosen target. The highest saturated capacity of p‐dihydroxybenzene of β‐CD‐CTS and β‐CD‐6‐CTS were 51.68 and 46.41 mg/g, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 860–864, 2004     

Two‐Phase Hydroformylation of Higher Olefins Using Randomly Methylated α‐Cyclodextrin as Mass Transfer Promoter: A Smart Solution for Preserving the Intrinsic Properties of the Rhodium/Trisulfonated Triphenylphosphine Catalytic System

The two‐phase hydroformylation of higher olefins with the rhodium/trisulfonated triphenylphosphine catalytic system in the presence of various chemically modified α‐cyclodextrins has been investigated. These cyclodextrins allowed us to increase greatly the reaction rate and the chemoselectivity of the reaction but, contrary to what has been observed previously with the chemically modified β‐cyclodextrins, the linear to branched aldehydes ratio was not affected by the presence of α‐cyclodextrin derivatives. Indeed, the latter was found to be similar to that obtained without any mass transfer promoter, suggesting that the catalytic species are stable in the presence of α‐cyclodextrin derivatives.     

Hydrophobically modified poly[(divinyl ether)‐co‐(maleic anhydride)]: interactions with cyclodextrin derivatives and hydrogel formation

Hydrolyzed cyclocopolymer prepared from divinyl ether and maleic anhydride, poly[(divinyl ether)‐ co ‐(maleic anhydride)] (DIVEMA), was functionalized with aminoadamantane and subsequently compared with the hydrolyzed DIVEMA with respect to physicochemical properties. The complexation behavior of adamantyl modified DIVEMA with cyclodextrin derivatives was examined by dynamic light scattering, nuclear magnetic resonance spectroscopy and zeta potential. The scattering studies indicated the formation of well‐defined aggregated structures with an average diameter of 120 nm. These aggregated structures collapsed on addition of randomly methylated β‐cyclodextrin to give 4.2 nm in hydrodynamic diameter. Interactions with crosslinked β‐cyclodextrins indicated gel formation which was analyzed by means of rheology and temperature‐dependent viscosity showing disaggregation of the host‐guest system at 42 °C. This novel physical hydrogel is very interesting for medical applications as a drug delivery system with included anti‐tumor activity. Copyright © 2012 Society of Chemical Industry     

3,5‐Bis(n‐perfluorooctyl)benzyltriethylammonium Bromide (F‐TEBA): An Efficient,Easily Recoverable Fluorous Catalyst for Solid‐Liquid PTC Reactions

A readily available 3,5‐bis(perfluorooctyl)benzyl bromide and triethylamine were reacted under mild conditions to give 3,5‐bis(n‐perfluorooctyl)benzyltriethylammonium bromide ( F‐TEBA ), an analogue of the versatile phase‐transfer catalyst, benzyltriethylammonium chloride (TEBA), containing two fluorous ponytails. This perfluoroalkylated quaternary ammonium salt was successfully employed as a catalyst in a variety of reactions run under solid‐liquid phase‐transfer catalysis (SL‐PTC) conditions. Thus, being both hydrophobic and lipophobic, F‐TEBA could be quickly recovered in quantitative yields, and reused without loss of activity over several reaction cycles.     

Synthesis of a novel linear water‐soluble β‐cyclodextrin polymer

A novel linear water‐soluble β‐cyclodextrin polymer has been prepared by grafting β‐cyclodextrin on poly[(methyl vinyl ether)‐alt‐(maleic anhydride)]. First, lithium hydride was used to obtain the mono‐alkoxide β‐CD. Grafting of β‐CD derivatives to the polymer backbone was then carried out by an esterification method. Using this method, polymers containing various amounts of β‐CD were synthesized. The resulting grafted polymers were characterized by two complementary methods, ¹H NMR and IR spectroscopy. The first was used to calculate the degree of substitution for the low amounts of β‐CD. The second method was very useful to evaluate the degree of substitution and the molar ratio of CD especially for high amounts of grafting. Our results indicate good agreement between both methods for intermediate rates. Copyright © 2004 Society of Chemical Industry     

Coating of porous silica beads by in situ polymerization/crosslinking of 2‐hydroxypropyl β‐cyclodextrin for reversed‐phase high performance liquid chromatography applications

Porous silica beads were coated with a crosslinked β‐cyclodextrin polymer by in situ polymerization/crosslinking of 2‐hydroxypropyl β‐cyclodextrin with 1,6‐hexamethylenediisocyanate in anhydrous dimethylsulfoxide. This method was developed for the preparation of reversed‐phase high performance liquid chromatography stationary phases. The mass of polymer immobilized onto the silica surface was controlled by the amount of coupling agent, 1,6‐hexamethylenediisocyanate, added during the coating process. The influence of the polymer coating on the physical features of the beads was investigated by means of nitrogen adsorption/desorption methods, scanning electron microscopy and energy dispersion X‐ray analysis. The column lifetime was found to be primarily dependent on the extent of crosslinking of the stationary phase. Moreover, it was demonstrated that the synthesis of highly crosslinked stationary phases with a reasonable column lifetime gave rise to a phase separation of the β‐cyclodextrin polymer. To prove their usefulness as reversed‐phase packing materials, they were used to separate mixtures of nitrophenol positional isomers, four pesticides, and drugs. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1419–1426, 2004     

Palladium(II)‐Catalyzed 1,4‐Addition of Arylboronic Acids to β‐Arylenones for Enantioselective Synthesis of 4‐Aryl‐4H‐chromenes

The enantioselective 1,4‐addition of arylboronic acids to β‐arylenones to give β‐diaryl ketones was carried out at 0–25 °C in the presence of a dicationic palladium(II) catalyst, [Pd(S,S‐chiraphos)(PhCN)₂](SbF₆)₂. Addition of a silver salt such as silver tetrafluoroborate [AgBF₄] or silver hexafluoroantimonate [AgSbF₆] (5–10 mol %) was effective to achieve high enantioselectivities at low temperatures (92–99 % ee) and to reduce the catalyst loading to 0.05 mol %. The protocol provided a simple access to 4‐aryl‐4H‐chromenes. Optically active chromenes were synthesized with up to 99 % ee via dehydration of the 1,4‐adducts between arylboronic acids and β‐(2‐hydroxyaryl)‐α,β‐unsaturated ketones.