Chiral Carbonates Research Articles

Mixed carbonates as useful substrates for a fluorogenic assay for lipases and esterases.

Mixed carbonates of 7-hydroxy-4-methylcoumarin were shown to be a new class of probe for fluorogenic assays. They are promising substrates for fingerprinting enzyme hydrolytic activity, and proved particularly useful because of the low level of nonspecific degradation and ease of synthesis. They are highly relevant for screening lipase and esterase libraries. These advantages make umbelliferyl carbonates highly suitable substrates for high-throughput screening. Moreover, we report the use of chiral fluorogenic carbonates as enantiopreference probes.

Dielectric relaxation modes in cholesteryl oleyl carbonate observed by non-linear dielectric spectroscopy

The non-linear dielectric spectra of chiral crystal cholesteryl oleyl carbonate (COC) were recorded in the frequency range of 1–100 MHz in the presence of strong static electric field V/m. The measurements were performed in the cholesteric nematic phase N*. The results revealed two regions in the temperature dependence of the chemical relaxation time behaviour, corresponding to two-phase coexistence region (blue phase + N*) and homogenous cholesteric phase N*, respectively. In the non-linear dielectric relaxation spectra, three absorption bands, related to the different molecular rotations of individual molecules around axes and director, have been observed. The negative components of the frequency dependence of the non-linear dielectric phenomena concern the Langevin saturation of the dipoles orientation in strong electric field.

Synthesis of chiral propylene carbonate via asymmetric ring opening of racemic propylene oxide by carbon dioxide on immobilized cobalt salen catalyst

Chiral Co(salen) complexes bearing Co(BF4)2 salt could efficiently catalyze the ring opening reaction of terminal epoxide by carbon dioxide in the presence of catalytic amounts of ionic liquid. The high amount loading of ionic liquid C6-IL as a co-catalyst led to the decrease the ee% of propylene carbonate (PC), but the conversion of propylene oxide (PO) has increased with the added amount. The homogeneous salen catalyst could be immobilized easily on the acidic sites of supports by non-covalent bonding, and exhibited moderate activity for producing enantiomerically enriched cyclic carbonates. The optically pure cyclic carbonates can be obtained by the catalytic resolution process resulting from HKR of racemic (±)PO in conjunction with CO2 coupling, as one-pot reaction. The presence of water improved the optical purity of final product PC in that system. The heterogenized chiral salen catalyst has retained the high activity in the repeated use, and no severe extraction of salen complexes from the support was found by using a heterogenized IL.

Chiral metal-containing ionic liquid: Synthesis and applications in the enantioselective cycloaddition of carbon dioxide to epoxides

A series of novel chiral metal-containing ionic liquids (CMILs) consisting of the cation of crown ether-chelated potassium/sodium and the anion of chiral amino acids were designed and synthesized. These new CMILs were used to catalyze the enantioselective cycloaddition of epoxides and carbon dioxide incorporating with the salenCo(OOCCCl3) to generate corresponding chiral cyclic carbonates under mild conditions. These new catalysts can be recycled at least five times without significant loss of activity and enantioselectivity.

Dimers of cyclic carbonates: chirality recognition in battery solvents and energy storage

Dimers of ethylene carbonate and propylene carbonate are created in supersonic jet expansions and characterized by FTIR spectroscopy. Fermi resonances are switched on and off by dimerization. There is a unique centrosymmetric dimer of ethylene carbonate in a pronounced case of complementary chirality synchronization, contributing to its energy storage capacity at melting. Two chiral propylene carbonate molecules combine in more intricate ways. If they have the same handedness, one of them is forced into an axial conformation and the binding partner stays in the more stable equatorial structure. If they have opposite handedness, centrosymmetric dimers of either axial or equatorial conformations are formed. This suggests the usefulness of chirality control in elucidating ionic transport mechanisms in battery solvents and asymmetric catalysis in such solvents.

ChemInform Abstract: Vinyl Carbonates as Novel Alkoxycarbonylation Reagents in Enzymatic Synthesis of Carbonates.

Abstract Carbonates could be obtained by enzymatic alkoxycarbonylation from vinyl carbonates, which are easily prepared from vinylchloroformate. The reaction was catalyzed by Candida antartica lipases, SP 435 and SP 435 A. The method could be also used for the synthesis of carbamates. When racemic alcohols were used, lipase catalyzed their resolution, and chiral carbonates were obtained with different enantiomeric excesses depending upon the structure of the alcohol.

ChemInform Abstract: Highly Regioselective Palladium-Mediated Substitution of Allylic and Dienylic Cyclic Carbonates.

Abstract Reaction of chiral allylic and dienylic cyclic carbonates with various nucleophiles in the presence of (PPh 3 ) 4 Pd as a catalyst afforded α-, γ-, or e-substituted products with high regio-, ( E )-stereo-, and diastereoselectivity depending on nucleophiles.

Cinchona-Derived Quaternary Ammonium Salts-Improved Asymmetric Cycloaddition of CO2 to Epoxides

Abstract A new catalyst system, SalenCoX/cinchona-derived quaternary ammonium salts, was developed to catalyze the cycloaddition of CO 2 to epoxides under extremely mild reaction conditions. Chiral propylene carbonate was obtained with good enantioselectivity in the presence of the catalyst. The anions of the catalyst and the cocatalyst evidently affect the activity and enantioselectivity of the reaction. The activity of ( S,S )-catalysts in terms of anion is in the order 2-nitrophenoxy > 2,4,6-trinitrophenoxy > NO 3 − > OAc − > CF 3 CO 2 − ≈ Br − > Cl − > OTs − . The cocatalyst with anion Cl − gives the highest ee value for propylene carbonate. In contrast, the cocatalyst with anion Br − has higher activity. When the catalyst ( S,S )-(+)-1,2-cyclohexanediamino( N,N -bis(3,5-di- tert -butyl-salicylidene) cobalt(III) acetate (( S,S )- A ) was combined with the cocatalyst N,O -dibenzylquininium chloride ( 1a ), it gives the highest 73% ee for propylene carbonate.

Bifunctional Chiral Catalyst for the Synthesis of Chiral Cyclic Carbonates from Carbon Dioxide and Epoxides

AbstractBifunctional chiral catalysts incorporating the N,N′‐bis(salicylidene)cyclohexenediaminato (salen) ligand and a quaternary onium salt within one metal complex were synthesized and developed for the catalytic kinetic resolution of racemic epoxides with carbon dioxide to generate chiral cyclic carbonates in high yield and with moderate enantioselectivity. These new catalysts also have a great advantage as they can be recycled without any obvious loss of activity and enantioselectivity.

Nonlinear Dielectric Relaxation in the Isotropic Phase and Mesophases of Cholesteryl Oleyl Carbonate

The nonlinear dielectric spectra of chiral crystal cholesteryl oleyl carbonate (COC) were recorded in frequency range of 1-100 MHz in the presence of the strong static electric field E(0) = 1 x 10(7) V/m. The measurements were performed within the temperature range of about 23 K in the isotropic, the blue phase, and the chiral nematic phase known also as the cholesteric phase. In the nonlinear dielectric relaxation spectra two absorption bands, related to molecular rotations (orientational band) and intermolecular interactions (chemical band), have been observed. The nonlinear dielectric results were interpreted by combination of a Debye-type and Coffey's equations, extended to the case of two simultaneous relaxation processes. The results revealed three regions in the temperature dependence of the chemical relaxation time behavior, corresponding to isotropic phase, blue phase and chiral nematic phase, respectively. Dynamic phenomena, observed in very narrow range of temperature (2 K) in the vicinity of the phase transition between the blue phase and the chiral nematic phase, were interpreted in frames of the Landau-de Gennes theory.

Catalytic Asymmetric Cycloaddition of Carbon Dioxide and Propylene Oxide Using Novel Chiral Polymers of BINOL‐Salen‐ Cobalt(III) Salts

Abstractmagnified imageFour new chiral polymers of BINOL‐Salen‐cobalt(III) salt complexes have been designed, synthesized and applied to the direct fabrication of chiral propylene carbonate from racemic propylene oxide. The (R/S)‐polymer catalyst 2 and (S/R)‐polymer catalyst 4 exhibit better enantioselectivity than the (R/R)‐polymer catalyst 1 and the (S/S)‐polymer catalyst 3 and have been recovered and reused more than ten times without loss of activity and enantioselectivity.

New Chiral Derivatizing Agents: Convenient Determination of Absolute Configurations of Free Amino Acids by 1H NMR

The chiral carbonate reagents 5 allow for the direct and unambiguous determination of the absolute configurations of a wide range of free amino acids using (1)H NMR. By using a approximately 3:1 mixture of (S)-5 and (R)-5, absolute configurations of the corresponding carbamates are determined by only analyzing the nitrogen protons.

Chiral ionic liquids improved the asymmetric cycloaddition of CO2 to epoxides

The new catalyst system of chiral SalenCo(OAc)/chiral ionic liquid was developed to catalyze the asymmetric cycloaddition reaction of CO2 and epoxides yielding the chiral cyclic carbonates. The synergistic effect between them is discussed.

Self-Assembly of a Chiral Carbonate- and Cytidine-Containing Dodecanuclear Copper(II) Complex: a Multiarm-Supplied Globular Capsule

A dodecanuclear copper(II) globular-shaped structure has been obtained with the cytidine nucleoside and the templating carbonate anion. It shows receptor properties through anion-cation and multiple anion-pi interactions toward ClO 4 (-) as well as an overall antiferromagnetic coupling.

Chiral catalysts for the asymmetric cycloaddition of carbon dioxide with epoxides

Several chiral BINADCo(III)X (BINAD = Bis(1,1′-2-hydroxy-2′-alkoxy-3-naphthylidene)-1,2-cyclohexanediamine, X = OAc, CF 3CO 2, CCl 3CO 2, OTs, p-NO 2PhCO 2) complexes were synthesized and used to catalyze the asymmetric cycloaddition of carbon dioxide with epoxides under mild condition to afford chiral cyclic carbonates. The best catalyst of ( S, S, S, S)-BINADCo(III)(OAc) 9b and phenyltrimethylammonium tribromide (PTAT) can provide propylene carbonate with the highest ee being 95% at −20 °C.

Copper-catalyzed substitution of allylic carbonates with diboron: A new approach to allylboronate synthesis

Abstract Copper-catalyzed γ-selective substitution of allylic carbonates with diboron provides a new method for the efficient synthesis of allylboronates. Optically active α-chiral allylboronates were synthesized through the reaction of chiral allylic carbonates with bis(pinacolato)diboron in the presence of achiral Cu(I)-catalyst with highly efficient chirality transfer. Additionally, in the presence of a chiral Cu(I) catalyst, optically active α-chiral allylboronates were obtained with >90 % ee through the reaction of prochiral substrates with the diboron.

Quaternary onium tribromide catalyzed cyclic carbonate synthesis from carbon dioxide and epoxides

Novel and efficient organic catalysts of quaternary onium tribromide and the related metal-containing catalysts of SalenCoX/PTAT were developed to catalyze the coupling reaction of carbon dioxide and epoxides generating relevant cyclic carbonates including chiral propylene carbonate under extremely mild condition.

Cu-Catalyzed Stereoselective Reaction of Allylic Carbonates with Diboronate

Allylboron derivatives are important synthetic intermediates, for instance, for the ste­reoselective allylation of carbonyl compounds. This is a new and very attractive method for a dia­stereoselective preparation of allylboron pinacolates, starting from readily available chiral allylic carbonates. The reaction conditions are extremely mild, and this process offers an excellent tolerance of functional groups. In the presence of ­Xanthphos as a ligand, the reaction is completely γ-selective. As expected, (Z)- and (E)-allylic carbonates with the same configuration of the chiral center give the opposite enantiomers of the product.

Palladium‐Catalyzed Carbon Dioxide Elimination—Fixation Reaction of 4‐Methoxycarbonyloxy‐2‐buten‐1‐ols.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium-catalyzed carbon dioxide elimination-fixation reaction of 4-methoxycarbonyloxy-2-buten-1-ols.

A new type of palladium-catalyzed CO(2) recycling reaction using allylic carbonates is described. Reaction of trans-4-methoxycarbonyloxy-2-buten-1-ols in the presence of a palladium catalyst produces cyclic carbonates having a vinyl group via a CO(2) elimination-fixation process. A variety of allylic carbonates participate in the reaction giving cyclic carbonates with high efficiencies. Stereoselective construction of trans-cyclic carbonates is achieved by using nonsymmetric substrates. An enantiospecific reaction proceeds to give chiral cyclic carbonate when a chiral methyl-substituted substrate is subjected to the reaction conditions.