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Recent attempts to mimic enzyme catalysis using simple, short peptides have been successful in enhancing various reactions, but the on‐demand, temporal or spatial regulation of such processes by external triggers remains a great challenge. Light irradiation is an ideal trigger for regulating molecular functionality, since it can be precisely manipulated in time and space, and because most reaction mediums do not react to light. We herein report the selection of a photo‐switchable amphiphilic peptide catalyst from a small library of isomeric peptides, each containing an azobenzene‐based light responsive group and a catalytic histidine residue. In its native fibrillar form, the selected peptide is efficiently and enantio‐selectively active for ester hydrolysis, but after irradiation by UV light inducing trans‐to‐cis azobenzene isomerization, the fibrils disassemble to amorphous aggregates that are much less catalytically active. Significantly, this esterase‐like activity can be manipulated multiple times, as the fibrillar peptide assembly is reversibly reduced and restored upon alternate irradiation by UV and visible light, respectively. We propose that this research may shine light on the origin of complex functions in early chemical evolution. Furthermore, it paves the way to regulate additional functions for peptide nanotechnology, such as replication, charge transfer, and delivery. [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHAs) have attracted broad interest as promising sustainable materials to address plastic pollution and resource scarcity. However, the chemical synthesis of stereoregular PHAs via ring‐opening polymerization (ROP) has long been an elusive endeavor. In this contribution, we exploited a robust spiro‐salen yttrium complex (Y3) as the catalyst to successfully prepare syndiotactic PHAs with diverse pendent groups. Simply altering the ratio of enantiomeric catalysts allowed to access of PHAs with diverse syndiotacticity (Pr=0.5–0.99, from sticky oil to tough materials), delivering tunable thermal properties (glass transition temperature, Tg from −52 to 70 °C and melting transition temperature, Tm from 38 to 223 °C). A combined experimental and computational study suggested a polymeric exchange mechanism could boost the polymerization activity and control the syndioselectivity. [ABSTRACT FROM AUTHOR]

A mild procedure for the diastereoselective preparation of functionalized 1,3-dienes and their synthetic versatility are described herein. The silver-catalyzed decomposition of α-diazo-γ,δ-unsaturated esters through β-hydride migration at room temperature resulted in the stereoselective formation of 12 conjugated (1 E ,3 E)-dienes. Further synthetic post-modifications included intramolecular Heck reaction and hydrogenation, leading to a novel substituted indene and an aliphatic diester, respectively. To rationalize the observed reaction outcome, a computational investigation of the mechanisms was conducted, emphasizing the importance of factors such as metallocarbenoid stability, substituent effects, and microkinetics simulations to better understand the reaction intricacies. [ABSTRACT FROM AUTHOR]

Synthesizing organocatalysts is often a long and cost-intensive process, therefore, the recovery and reuse of the catalysts are particularly important to establish sustainable organocatalytic transformations. In this work, we demonstrate the synthesis, application, and recycling of a new lipophilic cinchona squaramide organocatalyst. The synthesized lipophilic organocatalyst was applied in Michael additions. The catalyst was utilized to promote the Michael addition of cyclohexyl Meldrum’s acid to 4-chloro-trans-β-nitrostyrene (quantitative yield, up to 96% ee). Moreover, 1 mol % of the catalyst was feasible to conduct the gram-scale preparation of baclofen precursor (89% yield, 96% ee). Finally, thanks to the lipophilic character of the catalyst, it was easily recycled after the reaction by replacing the non-polar reaction solvent with a polar solvent, acetonitrile, with 91–100% efficiency, and the catalyst was reused in five reaction cycles without the loss of activity and selectivity.

A challenge in mimicking tyrosinase activity using model compounds is to reproduce its enantioselectivity. Good enantioselection requires rigidity and a chiral center close to the active site. In this study, the synthesis of a new chiral copper complex, [Cu2(mXPhI)]4+/2+, based on an m-xylyl-bis(imidazole)-bis(benzimidazole) ligand containing a stereocenter with a benzyl residue directly bound on the copper chelating ring, is reported. Binding experiments show that the cooperation between the two metal centers is weak, probably due to steric hindrance given by the benzyl group. The dicopper(II) complex [Cu2(mXPhI)]4+ has catalytic activity in the oxidations of enantiomeric couples of chiral catechols, with an excellent discrimination capability for Dopa-OMe enantiomers and a different substrate dependence, hyperbolic or with substrate inhibition, for the L- or D- enantiomers, respectively. [Cu2(mXPhI)]4+ is active in a tyrosinase-like sulfoxidation of organic sulfides. The monooxygenase reaction requires a reducing co-substrate (NH2OH) and yields sulfoxide with significant enantiomeric excess (e.e.). Experiments with 18O2 and thioanisole yielded sulfoxide with 77% incorporation of 18O, indicating a reaction occurring mostly through direct oxygen transfer from the copper active intermediate to the sulfide. This mechanism and the presence of the chiral center of the ligand in the immediate copper coordination sphere are responsible for the good enantioselectivity observed. [ABSTRACT FROM AUTHOR]

Enantioselective synthesis of chiral alcohols through asymmetric addition of water across an unactivated alkene is a highly sought‐after transformation and a big challenge in catalysis. Herein we report the identification and directed evolution of a fatty acid hydratase from Marinitoga hydrogenitolerans for the highly enantioselective hydration of styrenes to yield chiral 1‐arylethanols. While directed evolution for styrene hydration was performed in the presence of heptanoic acid to mimic fatty acid binding, the engineered enzyme displayed remarkable asymmetric styrene hydration activity in the absence of the small molecule activator. The evolved styrene hydratase provided access to chiral alcohols from simple alkenes and water with high enantioselectivity (>99 : 1 e.r.) and could be applied on a preparative scale. [ABSTRACT FROM AUTHOR]

Raw mixtures of Rare Earths Elements, REE, recovered by E-waste, were used as catalysts to promote the (stereoselective) synthesis of highly valuable compounds. Y 2 O 3 , the major species that is recovered by the E-waste, can be easily converted into the catalytically active Y(OTf) 3 that is able to efficiently promote the Michael addition of indoles to benzylidene malonates and the stereoselective Diels-Alder cycloaddition between cyclopentadiene and 4-(S)-3 acryloyl 4-tert-butyl 2-oxazolidinone. Additionally, the raw mixtures were immobilissed onto silica and used to construct packed reactors, resulting in values for Productivity and Space-Time Yields that were significantly higher than those of the corresponding batch conversions. Notably, the prepared cartridge employed in the model Michael reaction maintained its catalytic efficiency for more than 4 days of continuous running., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

• Green one-pot synthesis of triptycene derived three oligomers TOLs. • Characterization of TOLs using FT-IR, solid state 13C NMR, GPC and FESEM. • Exploration of TOLs as cobalt-based heterogeneous catalysts for the synthesis of oxindoles. • A thorough optimization of several reaction parameters, including solvent, temperature, and co-catalyst. • Investigation of substrate scope to achieve excellent yields (up to 99 %) with good dr (up to 99 %). Novel triptycene derived oligomers (TOL1, TOL2 and TOL3) with multiple metal-coordinating sites have been synthesized in high yields using a three-component one-pot synthetic protocol and were characterized by various analytical tools such as FT-IR, solid state 13C NMR, GPC and FESEM. The GPC analysis revealed TOLs as oligomers with 8-10 repeating units. The catalytic applications of these oligomers were investigated for the stereoselective synthesis of 3-hydroxy-2-oxindoles via aldol reaction of isatin with ketones by the in-situ complexation of the oligomers with Cobalt metal. All the tested reactions worked well to generate the corresponding products in excellent yields with good diastereo-selectivities. [Display omitted] [ABSTRACT FROM AUTHOR]

We report here on the ring‐opening polymerization (ROP) of racemic β‐thiobutyrolactone (rac‐TBL), as the first chemical synthesis of poly(3‐thiobutyrolactone) (P3TB), the thioester analogue of the ubiquitous poly(3‐hydroxybutyrate) (P3HB). The ROP reactions proceed very fast (TOF >12 000 h−1 at r.t.) in the presence of various metal‐based catalysts. Remarkably, catalyst systems based on non‐chiral yttrium complexes stabilized by tetradentate amino alkoxy‐ or diamino‐bis(phenolate) ligands {ONXOR1,R2}2− (X=O, N) provide access to cyclic P3TB with either high isoselectivity (Pm up to 0.90) or high syndiotactic bias (Pr up to 0.70). The stereoselectivity can be controlled by manipulation of the substituents on the ligand platform and adequate choice of the reaction solvent and temperature as well. The cyclic polymer topology is evidenced by MALDI‐ToF MS, NMR and TGA. Highly isotactic cyclic P3TB is a semi‐crystalline material as revealed by DSC. [ABSTRACT FROM AUTHOR]

Overcrowded alkenes are expeditiously prepared by the versatile Barton–Kellogg olefination and have remarkable applications as functional molecules owing to their unique stereochemical features. The induced stereodynamics thereby enable the controlled motion of molecular switches and motors, while the high configurational stability prevents undesired isomeric scrambling. Bistricyclic aromatic enes are prototypical overcrowded alkenes with outstanding stereochemical properties, but their stereocontrolled preparation was thus far only feasible in stereospecific reactions and with chiral auxiliaries. Herein we report that direct catalyst control is achieved by a stereoselective Barton–Kellogg olefination with enantio‐ and diastereocontrol for various bistricyclic aromatic enes. Using Rh2(S‐PTAD)4 as catalyst, several diazo compounds were selectively coupled with a thioketone to give one of the four anti‐folded overcrowded alkene stereoisomers upon reduction. Complete stereodivergence was reached by catalyst control in combination with distinct thiirane reductions to provide all four stereoisomers with e.r. values of up to 99:1. We envision that this strategy will enable the synthesis of topologically unique overcrowded alkenes for functional materials, catalysis, energy‐ and electron transfer, and bioactive compounds. [ABSTRACT FROM AUTHOR]

Poly(hydroxy acid)s are a family of biocompatible and (bio)degradable polyesters with various outcomes in different domains of application. To date, poly(hydroxy acid)s are best prepared by ring‐opening polymerization (ROP) of the corresponding cyclic esters. Using racemic chiral monomers featuring side‐chain groups enables to access, providing a stereoselective catalyst/initiator system is implemented, stereoregular functional polymers, thereby improving their physico–chemical properties, and ultimately, widening their range of uses. Here, we highlight a few important advances in metal‐mediated stereoselective ROP of cyclic esters towards the synthesis of (functional) stereoregular poly(hydroxy acid)s that have recently been disclosed, emphasizing on (functional) β‐ and γ‐lactones, diolide and O‐carboxyanhydride (OCA) monomers and yttrium‐based catalysis. Fine‐tuning of the substituents flanked on the catalyst ligand enables reaching poly(hydroxy acid)s with syndiotactic and also isotactic microstructures. The stereocontrol mechanisms at work and their probable origin, relying on steric but also electronic factors imparted in particular by the ligand substituents, are discussed. Taking advantage of such stereoselective ROPs, original copoly(hydroxy acid)s with gradient or alternated patterns then become accessible from the use of mixtures of chemically different, oppositely configured enantiopure monomers. [ABSTRACT FROM AUTHOR]

The arene-forming aldol condensation is a fundamental reaction in the biosynthesis of aromatic polyketides. Precisely controlled by the polyketide synthases, the highly reactive poly-β-carbonyl substrates are diverged into numerous aromatic natural products by selective cyclization reactions; a fascinating biosynthetic strategy that sparked our interest to investigate atroposelective aldol condensations. In this Account, we contextualize and highlight the ability of small-molecule catalysts to selectively convert noncanonical hexacarbonyl substrates in a double arene-forming aldol condensation resulting in the atroposelective synthesis of tetra- ortho -3,3′-substituted biaryls. The hexacarbonyl substrates were obtained by a fourfold ozonolysis enabling a late-stage introduction of all carbonyl functions in one step. Secondary amine catalysts capable of forming an extended hydrogen-bonding network triggered the noncanonical polyketide cyclization in order to form valuable biaryls in high yields and with stereocontrol of up to 98:2 er. 1 Biosynthesis of Aromatic Polyketides 2 Rotationally Restricted Aromatic Polyketides 3 3,3′-Substituted Binaphthalenes in Catalysis 4 Stereoselective Synthesis of Atropisomers 5 Synthesis of Enantioenriched Tetra- ortho -3,3′-Substituted Biaryls by the Atroposelective Arene-Forming Aldol Condensation 6 Conclusion [ABSTRACT FROM AUTHOR]

Ring-opening polymerization (ROP) of cyclic esters/lactones by efficient catalysts is a powerful method for synthesis of biodegradable and biocompatible polyesters with well-defined structures. To develop catalytic systems that are fast, selective and controlled is a persistent effort of chemists. In this contribution, we report a binary urea/alkoxide catalytic system that could catalyze ROP of rac-LA in a fast (over 90% conversion within 1–2 min), stereoselective (Pi up to 0.93) and controlled manner, indicated by narrow MW distributions, linear relationship between the monomer conversions and Mns, end-group fidelity, and chain extension experiments. Remarkably, the catalytic system described here is simple, easily prepared, and structurally tunable and thus has versatile catalytic performances.

Abstract: Acid‐modified halloysite nanotubes were used for the first time as a stereoselective catalyst for synthesis of oxygen‐containing heterocycles applying of allyl alcohol (−)‐isopulegol condensation with aldehydes to the octahydro‐2H‐chromenol (4R‐ and 4S‐diastereomers) as an example. The catalysts were characterized by XRF, XRD, N2‐adsorption, FTIR with pyridine and MAS NMR methods. A high ratio of 4R/4S diastereomers (7.6–14.5) under mild conditions in cyclohexane was considerably exceeding previously reported results. Unprecedented selectivity (79–83 %) to 4R isomer of thiophenyl‐substituted chromenol exhibiting high analgesic activity was achieved. An increase in stereoselectivity with a decrease in the halloysite drying temperature and catalyst acidity clearly indicates formation of 4R diastereomer on the weak Brønsted sites. This work is an example that control of the stereoselectivity of acid‐catalyzed organic reactions can be effectively carried out by varying water content on the aluminosilicate surface. Modified halloysite nanotubes can be considered as extremely promising catalysts for stereoselective synthesis of heterocyclic compounds. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and structures of the first SiII‐donor supported manganese(II) complexes [L1]MnCl2, [L2]MnCl2, and [L3]2MnCl2 are reported, bearing a pincer‐type bis(NHSi)‐pyridine ligand L1, bidentate bis(NHSi)‐ferrocene ligand L2, and two monodentate NHSi ligands L3 (NHSi = N‐heterocyclic silylene), respectively. They act as unprecedented very active and stereoselective Mn‐based precatalysts (1 mol % loading) in transfer semi‐hydrogenations of alkynes to give the corresponding E‐olefins using ammonia–borane as a convenient hydrogen source under mild reaction conditions. Complex [L1]MnCl2 shows the best catalytic performance with quantitative conversion rates and excellent E‐stereoselectivities (up to 98 %) for different alkyne substrates. Different types of functional groups can be tolerated, except CN, NH2, NO2, and OH groups at the phenyl group of 1‐phenyl substituted alkynes. [ABSTRACT FROM AUTHOR]

By taking inspiration from the fascinating biosynthetic machinery that creates aromatic polyketides, our group investigates analogous reactions catalyzed by small molecules. We are particularly captivated by the prospects of intramolecular aldol condensation reactions to generate different rotationally restricted aromatic compounds. In a first project of our independent research group, a highly stereoselective amine catalyzed synthesis of axially chiral biaryls, tertiary aromatic amides and oligo-1,2-naphthylenes has been developed. In this article, we outline the twists and turns for our escape from the aromatic flatland to structurally intriguing chiral arene scaffolds relevant for various fields of application.

Reported herein is the first stereoselective controlled ROP of a specific family of racemic functional β-lactones, namely 4-alkoxymethylene-β-propiolactones (BPLORs). This process is catalyzed by an yttrium complex stabilized by a nonchiral tetradentate amino alkoxy bisphenolate ligand {ONOOR′2}2−, which features both a good activity and a high degree of control over the molar masses of the resulting functional poly(3-hydroxyalkanoate)s. A simple modification of the R′ substituents in ortho and para position on the ligand platform allows for a complete reversal from virtually pure syndioselectivity (Ps up to 0.91 with R′=cumyl) to very high isoselectivity (Pi up to 0.93 with R′=Cl), as supported by DFT insights. This is the first example of a highly isoselective ROP of a racemic chiral β-lactone. [ABSTRACT FROM AUTHOR]

3D-printed flow reactors were designed, fabricated from different materials (PLA, HIPS, nylon), and used for a catalytic stereoselective Henry reaction. The use of readily prepared and tunable 3D-printed reactors enabled the rapid screening of devices with different sizes, shapes, and channel dimensions, aimed at the identification of the best-performing reactor setup. The optimized process afforded the products in high yields, moderate diastereoselectivity, and up to 90 % ee. The method was applied to the continuous-flow synthesis of biologically active chiral 1,2-amino alcohols (norephedrine, metaraminol, and methoxamine) through a two-step sequence combining the nitroaldol reaction with a hydrogenation. To highlight potential industrial applications of this method, a multistep continuous synthesis of norephedrine has been realized. The product was isolated without any intermediate purifications or solvent switches. [ABSTRACT FROM AUTHOR]

This contribution presents an updated overview of the different copolymers containing stereoregular polystyrene blocks. Special emphasis is placed on syndiospecific and isospecific copolymerization of styrene with co-monomers (ethylene and α-olefins, conjugated and non-conjugated dienes, styrene derivatives, etc.). The catalytic systems involved are described and the polymerization mechanisms are discussed. Alternative approaches (simultaneous, living, chain-transfer and graft copolymerization) and the resulting detailed structures and characteristics of the copolymers are also reported. [ABSTRACT FROM AUTHOR]

A series of magnesium silylamido complexes supported by tetradentate aminophenolate ligands, LMgN(SiMe 3 ) 2 (L = {(2-R 1 )Ar-CH 2 N[(CH 2 ) 2 R 2 ]CH 2 -(4-R 4 -6-R 3 )C 6 H 2 O − }, R 1 = NMe 2 , R 2 = N i Pr 2 , R 3 = R 4 = Cl ( 1 ), R 3 = R 4 = cumyl ( 2 ); R 1 = NMe 2 , R 2 = NEt 2 , R 3 = R 4 = cumyl ( 3 ), R 3 = CPh 3 , R 4 = Me ( 4 ); R 1 = NEt 2 , R 2 = NEt 2 , R 3 = CPh 3 , R 4 = Me ( 5 ); R 1 = NMe 2 , R 2 = ( S )-1-butylpyrrolidine-2-yl, R 3 = R 4 = cumyl ( 6 ), R 3 = CPh 3 , R 4 = Me ( 7 )), were synthesized and fully characterized, and their catalytic behaviors for the ring-opening polymerization (ROP) of rac -lactide ( rac -LA) were explored. The monomeric nature and versatile coordination modes of these complexes in the solid state were further confirmed by X-ray diffraction studies on complexes 1 , 3 and 7 . In complex 1 , the N , N -diisopropylamino group on the alkylamino side arm does not coordinate to the metal centre, whilst the remaining three donors of the aminophenolate ligand and the silylamido group bond with the magnesium centre. By contrast, in complexes 3 and 7 , the arylamino moiety does not coordinate to the metal centre, while the alkylamino side arm coordinates. It is worth noting that the introduction of the N , N -dimethyl amino group to the pendant benzyl group realises the diastereoselective synthesis of multichiral aminophenolate magnesium complexes, which has not been achieved by the corresponding tridentate aminophenolate ligand. It was found that most of these magnesium complexes serve as highly active initiators for the ROP of rac -LA. The coordination pattern of the aminophenolate ligand exerted a considerable influence on the activity and stereoselectivity of the corresponding complex toward the polymerization of rac -LA, leading to the production of moderate to high heterotactic biased PLAs. The enantiopure complex 7 showed the highest heteroselectivity among these magnesium complexes ( P r = 0.80 in toluene, P r = 0.82 in THF). [ABSTRACT FROM AUTHOR]

Catalysis by small molecules (≤1000 Da, 10−9 m) that are capable of binding and activating substrates through attractive, noncovalent interactions has emerged as an important approach in organic and organometallic chemistry. While the canonical noncovalent interactions, including hydrogen bonding, ion pairing, and π stacking, have become mainstays of catalyst design, the cation-π interaction has been comparatively underutilized in this context since its discovery in the 1980s. However, like a hydrogen bond, the cation-π interaction exhibits a typical binding affinity of several kcal mol−1 with substantial directionality. These properties render it attractive as a design element for the development of small-molecule catalysts, and in recent years, the catalysis community has begun to take advantage of these features, drawing inspiration from pioneering research in molecular recognition and structural biology. This Review surveys the burgeoning application of the cation-π interaction in catalysis. [ABSTRACT FROM AUTHOR]

The reductive amination of (−)-2-carene-3-aldehyde, prepared in two steps from (−)-perillaldehyde, furnished 2-carene-based allylamines. tert-Butyloxycarbonyl (Boc) or carbobenzyloxy (Cbz) protection of the resulting amines, followed by stereoselective dihydroxylation in highly stereospecific reactions with OsO4 and subsequent deprotection, resulted in N-benzylaminodiols, which were transformed to primary and tertiary aminodiols. The reactions of the N-benzyl- and N-(1-phenylethyl)-substituted derivatives with formaldehyde led to highly regioselective ring closure, resulting in carane-fused 1,3-oxazines. The aminodiols and their 1,3-oxazine derivatives were applied as chiral catalysts in the enantioselective addition of diethylzinc to aldehydes. The best ( R) enantioselectivity was observed in the case of the N-(( R)-1-phenylethyl)-substituted aminodiol, whereas the opposite chiral direction was preferred when the 1,3-oxazines were applied. Through the use of molecular modelling at an ab initio level, this phenomenon was interpreted in terms of competing reaction pathways. Molecular modelling at the RHF/LANL2DZ level of theory was successfully applied for a mechanism-based interpretation of the stereochemical outcome of the reactions leading to the development of further 1,3-oxazine-based ligands, which display excellent ( S) enantioselectivity (95 and 98 % ee) in the examined transformation. [ABSTRACT FROM AUTHOR]

Alkyl aluminum complexes of chiral salan ligands assembled around the 2,2'-bipyrrolidine core form as single diastereomers that have identical configurations of the N donors. Active catalysts for the polymerization of lactide were formed upon the addition of benzyl alcohol. Polymeryl exchange between enantiomorphous aluminum species had a dramatic effect on the tacticity of the poly(lactic acid) (PLA) in the polymerization of racemic lactide (rac-LA): The enantiomerically pure catalyst of the nonsubstituted salan ligand led to isotactic PLA, and the racemic catalyst exhibited lower stereocontrol. The enantiomerically pure catalyst of the chloro-substituted salan ligand led to PLA with a slight tendency toward heterotacticity, whereas the racemic catalyst led to PLA of almost perfect heterotacticity following an insertion/auto-inhibition/exchange mechanism. [ABSTRACT FROM AUTHOR]

The first modular and flexible synthesis of core-chiral bispidines was achieved by using an 'inside-out' strategy. The key intermediate, a NBoc-activated bispidine lactam, was constructed in enantiomerically pure form from a chirally modified β-amino acid and 2-(acetoxymethyl)acrylonitrile in just five steps and good 48 % yield. A simple addition-reduction protocol permitted a highly endo-selective introduction of substituents and, thus, a fast and variable access to 2- endo-substituted and 2- endo, N-fused bi- and tricyclic bispidines. The new diamines were evaluated as the chiral ligands in asymmetric Henry reactions. Excellent enantioselectivities of up to 99 % ee and good diastereomeric ratios of up to 86:14 were reached with a copper(II) complex modified by a 2- endo, N-(3,3-dimethylpyrrolidine)-annelated bispidine. Its performance is superior to that of the well-known bispidines (−)-sparteine and the (+)-sparteine surrogate. [ABSTRACT FROM AUTHOR]

Excellent catalytic stereoselectivity (up to > 99:1) with good yields (up to 88%) for Mannich reaction process under the solvent-free conditions at room temperature has been developed. [Display omitted] A series of indole-based organocatalysts (4b,9b-aryl-4b,5,9b,10-tetrahydroindolo[3,2- b ]indole derivatives) (2a-2f) have been designed and synthesized for the three-component direct Mannich reaction of aromatic aldehydes and aromatic amines with ketones. Significantly, the organocatalyst 2a delivered excellent catalytic stereoselectivity (up to >99:1) with good yields (up to 88 %) for above reaction process under the solvent-free conditions at room temperature. X-ray diffraction analysis reveals that organocatalyst 2a is of eight-membered central ring structure with interesting strained quadricyclic ring connectivity. The characteristic rigid V-shape indole ring structure contained in 2a and the formed hydrogen-bonding interaction between 2a and intermediate prefer to the anti-stereoselective product. [ABSTRACT FROM AUTHOR]

Silyl ketene imines derived from a variety of α-branched nitriles have been developed as highly useful reagents for the construction of quaternary stereogenic centers via the aldol addition reaction. In the presence of SiCl4 and the catalytic action of a chiral phosphoramide, silyl ketene imines undergo extremely rapid and high yielding addition to a wide variety of aromatic aldehydes with excellent diastereo- and enantioselectivity. Of particular note are the high yields and selectivities obtained from electron-rich, electron-poor, and hindered aldehydes. Linear aliphatic aldehydes did react with good diastereo- and enantioselectivity in the presence of nBu4N+I−, but branched aldehydes were much less reactive. Semiempirical calculations provided a rationalization of the observed diastereo- and enantioselectivity via open transitions states. [ABSTRACT FROM AUTHOR]

The boronic acid-catalyzed annulation of citral opens up a short route to oxygenated cyclized monoterpenoid pyranocarbazole alkaloids. Thus, murrayamine-D is available in only three steps and 55% overall yield from the corresponding carbazole precursor. [ABSTRACT FROM AUTHOR]

A process for the production of poly(lactic acid) with a melting point of > 150 °C from racemic lactide was developed. Only process steps that are usable in an industrial process were included to ensure an easy transfer to a commercial scale. A stereoselective catalyst system for lactide melt phase polymerization comprising of an Al-salen initiator, a hydroxyl cocatalyst and an acidic quenching additive was developed. Monomer recovery aspects, temperature variation and different catalyst concentrations were evaluated to allow for a high yield process which can be transferred to a technical scale. [ABSTRACT FROM AUTHOR]

Homolargazole derivatives, in which the macrocycle of natural largazole is extended by one methylene group, were prepared by the recently developed rhodium-catalyzed hydrocarboxylation reaction onto allenes. This strategy gives access to both the (18 S)- and (18 R)-stereoisomers in high stereoselectivity under ligand control. [ABSTRACT FROM AUTHOR]

Tuning the organocatalyst: An unprecedented enantioselective intramolecular oxa‐Michael reaction of unactivated α,β‐unsaturated amides and esters catalyzed by a powerful hydrogen‐bond‐donating organocatalyst has been developed. Furthermore, the products obtained from this reaction have been used for the straightforward asymmetric synthesis of several natural products and biologically important compounds. [ABSTRACT FROM AUTHOR]

CC coupling: DiPPAM 1 and BINAP 2 ligands led to divergent behaviors in the asymmetric conjugate addition (ACA) of dialkylzinc reagents to linear aryldienones, which were applied to the development of a highly selective sequential asymmetric 1,6/1,4‐ACA process (see scheme; Tf = triflate, DBU = 1,8‐diazabicyclo[5.4.0]undec‐7‐ene). [ABSTRACT FROM AUTHOR]

The article presents a study regarding the stereoselective ortho-Lithiation and catalytic ortho-Lithiation of a Ferrocene derivative. It mentions the proposed selectivity and catalytic activity of tetramethyl-1,2-cyclohexanediamine (TMCDA) was elucidated through the quantum-chemical calculations. The result of the study shows that the release of the chiral promoter form the lithiated species was made possible by the catalytic cycle.

A 1:1 mixture of [AuCl(IPr)] (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidine) and AgClO4 catalyzes the intermolecular dehydrative alkoxylation of primary and secondary allylic alcohols with aliphatic primary and secondary alcohols to form allylic ethers. These transformations are regio- and stereospecific with preferential addition of the alcohol nucleophile at the γ-position of the allylic alcohol syn to the departing hydroxyl group and with predominant formation of the E stereoisomer. The minor α regioisomer is formed predominantly through a secondary reaction manifold involving regioselective γ-alkoxylation of the initially formed allylic ether rather than by the direct α-alkoxylation of the allylic alcohol. [ABSTRACT FROM AUTHOR]

Allylic alcohols represent an important and highly versatile class of chiral building blocks for organic synthesis. This Review summarizes the plethora of methods developed for the catalytic asymmetric synthesis of enantioenriched allylic alcohols. These include: dynamic kinetic resolution (DKR/DKAT), nucleophilic 1,2-addition to carbonyl groups, allylic substitution, oxidation of CH bonds, the addition of O nucleophiles to π systems, reduction of unsaturated carbonyl compounds, and an alternative route from enantioenriched propargylic alcohols. Furthermore, these catalytic asymmetric processes are exemplified by their applications in the syntheses of complex molecules such as natural products and potential therapeutic agents. [ABSTRACT FROM AUTHOR]

A detailed account of the enantioselective total synthesis of (-)-zampanolide, a macrolide marine natural product with high anticancer activity, is described. For the synthesis of the 4-methylenetetrahydropyran unit of (-)-zampanolide, we initially relied upon an oxidative C-H activation of an alkenyl ether and intramolecular cyclization to provide the substituted tetrahydropyran ring. However, this strategy was unsuccessful. Subsequently, we found that a cinnamyl ether is critical for the successful oxidative intramolecular cyclization reaction. The synthesis also features a cross-metathesis reaction for the construction of a trisubstituted olefin, a ring-closing metathesis to form a highly functionalized macrolactone, and a chiral phosphoric acid promoted formation of an N-acyl aminal to furnish (-)-zampanolide stereoselectively and in good yield. The synthetic (-)-zampanolide had effects on cultured cells and on tubulin assembly consistent with the properties reported for the natural product. [ABSTRACT FROM AUTHOR]

A bimetallic heme-DNA cofactor, containing an iron and a copper center, was synthesized for the design of novel hybrid catalysts for stereoselective synthesis. The cofactor was used for the reconstitution of apo-myoglobin. Both the cofactor alone and its myoglobin adduct were used to catalyze a model Diels Alder reaction. Stereoselectivity of this conversion was analyzed by chiral HPLC. Reactions carried out in the presence of myoglobin-heme-Cu-DNA catalyst showed greater product conversion and stereoselectivity than those carried out with the heme-Cu-DNA cofactor. This observation suggested that the protein shell plays a significant role in the catalytic conversion. [ABSTRACT FROM AUTHOR]

Abstract: Two different parts of Candida antarctica lipase B (stereospecificity pocket at the bottom of the active site and hydrophobic tunnel leading to the active site) were redesigned by single- or double-point mutations, in order to better control and improve enzyme enantioselectivity toward secondary alcohols. Single-point isosteric mutations of Ser47 and Thr42 situated in the stereospecificity pocket gave rise to variants with doubled enantioselectivity toward pentan-2-ol, in solid/gas reactor. Besides, the width and shape of the hydrophobic tunnel leading to the active site was modified by producing the following single-point mutants: Ile189Ala, Leu278Val and Ala282Leu. For each of these variants a significant modification of enantioselectivity was observed compared to wild-type enzyme, indicating that discrimination of the enantiomers by the enzyme could also arise from their different accessibilities from the enzyme surface to the catalytic site. [Copyright &y& Elsevier]

Abstract: The effect of water activity (a W) on Candida antarctica lipase B (CALB) activity and enantioselectivity towards secondary alcohols was assessed. Experimental results for the resolution of racemic pentan-2-ol, hexan-3-ol, butan-2-ol and octan-4-ol by immobilized CALB-catalyzed acylation with methyl propanoate were obtained by using a solid/gas reactor. Water and substrate adsorption mechanism on immobilized CALB were then studied using moisture sorption analyzer and inverse gas chromatography, and the effective hydration state of the biocatalyst when varying a W was defined. The data showed a pronounced a W effect on both activity and enantioselectivity. If secondary alcohol follows the steric rules for being efficiently resolved, water at very low a W increased enantioselectivity by acting predominantly as an enantioselective inhibitor, making the stereospecificity pocket smaller. When increasing a W, water decreased enantioselectivity, due to an unfavourable increase of the entropic term TΔ R−S ΔS ‡ of the differential free energy of activation. The “turning point” at which water changed from one predominant role to another would correspond to a W allowing full coverage of polar groups of the immobilized biocatalyst by water molecules. [Copyright &y& Elsevier]

Highly efficient stereoselective 1.4-addition of racemic α-fluoro-αnitro(phenylsulfonyl)methane (FNSM) as a fluoromethyl pronucleophile to α,β-unsaturated ketones using a wide range of chiral organobifunctional catalysts under moderate conditions in the absence of an additional base has been achieved. A series of catalysts was screened for the enantioselective addition of FNSM to chalcones and the catalysts CN I. CD I, QN l-IV, and QD I were found to enable this reaction, successfully providing exclusive 1,4-addition products stereoselectively in high yields (conversion, diastereomeric ratio, and enantiomeric excess). Studies involving a model reaction and systematic analysis of the absolute configuration support the suggested mechanism. [ABSTRACT FROM AUTHOR]