One-step synthesis of sequence-controlled multiblock polymers with up to 11 segments from monomer mixture

Switchable polymerization holds considerable potential for the synthesis of highly sequence-controlled multiblock. To date, this method has been limited to three-component systems, which enables the straightforward synthesis of multiblock polymers with less than five blocks. Herein, we report a self-switchable polymerization enabled by simple alkali metal carboxylate catalysts that directly polymerize six-component mixtures into multiblock polymers consisting of up to 11 blocks. Without an external trigger, the catalyst polymerization spontaneously connects five catalytic cycles in an orderly manner, involving four anhydride/epoxide ring-opening copolymerizations and one L-lactide ring-opening polymerization, creating a one-step synthetic pathway. Following this autotandem catalysis, reasonable combinations of different catalytic cycles allow the direct preparation of diverse, sequence-controlled, multiblock copolymers even containing various hyperbranched architectures. This method shows considerable promise in the synthesis of sequentially and architecturally complex polymers, with high monomer sequence control that provides the potential for designing materials.

Synthetic and biosynthetic methods for selective cyclisations of 4,5-epoxy alcohols to tetrahydropyrans

In this review, methods for the selective intramolecular epoxide ring opening (IERO) of 4,5-epoxy-alcohols are discussed as well as biosynthetic pathways to tetrahydropyran-containing natural products which utilise IERO reactions.

Synthesis of trans N-Substituted Pyrrolidine Derivatives Bearing 1,2,4-triazole Ring

Background: 1,2,4-triazoles scaffolds display significant biological activities due to hydrogen bonding, solubility, dipole character, and rigidity Objective: The core motif of 1,2,4-triazoles plays a vital role in clinical drugs such as Rizatriptan (anti-migraine), Ribavirin (antiviral), anastrozole (anticancer), etizolam (anxiolytic), estazolam (anticonvulsant), alprazolam (anti-hypnotic), letrozole (aromatase inhibitor), loreclezole (anticonvulsant), trazadone (antidepressant) etc Method: Epoxide ring opening of tert-butyl 6-oxa-3-azabicyclo [3.1.0] hexane-3-carboxylate followed by methylation under basic conditions and de-protection gave the corresponding trans 1-(4-methoxypyrrolidin-3-yl)-1H-1,2,4-triazole hydrochloride salt as the precursor. This precursor on reaction with substituted benzoyl chlorides and benzyl bromides gave the desired amide and amine products Results: A library of 14 N-substituted pyrrolidine derivatives i.e. trans3-methoxy-4-(1H-1,2,4-triazol-1-yl) pyrrolidin-1-yl) (phenyl)methanone and trans 1-benzyl-4-methoxypyrrolidin-3-yl)-1H-1,2,4-triazole were prepared Conclusion: Eight novel amides (6a-h) and six amines (8a-f) derivatives were synthesized using 1-(4-methoxypyrrolidin-3-yl)-1H-1,2,4-triazole 4 salt with substituted benzoyl chlorides and benzyl bromides.

Synthesis of the Macrolactone Cores of Maltepolides via a Diene–Ene Ring-Closing Metathesis Strategy

Synthesis of the C19-truncated maltepolide E has been accomplished via a diene–ene RCM strategy without damage to the C11–C14 alkenyl epoxy unit. Upon release of the C17-OH group, it attacked at the C14 position with double bond migration and epoxide ring-opening to furnish the C19-truncated maltepolide A and B as proposed for the biosynthesis of maltepolides. Preliminary cytotoxicity data of the synthesized C19-truncated maltepolides against L929 mouse fibroblast cell line suggest irrelevance of the vinyl epoxide and importance of the conjugated dienyl keto unit for the observed anticancer activity.

Stereospecific Epoxidation of Limonene Catalyzed by Peroxygenase from Oat Seeds

Limonene is one of the most abundant naturally occurring cyclic monoterpenes and has recently emerged as a sustainable alternative to petroleum-based solvents as well as a chemical platform for the production of value-added compounds. The biocatalytic epoxidation of both enantiomers of limonene was carried out in the presence of a peroxygenase-containing preparation from oat (Avena sativa) flour. Different reaction profiles were observed depending on the starting enantiomer of limonene, but in both cases the 1,2-monoepoxide was obtained as the main product with excellent diastereoselectivity. Trans-1,2-monoepoxide and cis-1,2-monoepoxide were isolated from the reaction of (R)-limonene and (S)-limonene, respectively, and the reactions were scaled-up to 0.17 M substrate concentration. The process is valuable for operational simplicity, lack of toxic metal catalysts, and cost-effectiveness of the enzymatic source. Pure stereoisomers of 1,2-monoepoxides of limonene constitute a useful starting material for biorenewable polymers, but can be also converted into other chiral derivatives by epoxide ring opening with nucleophiles. As a proof of concept, a tandem protocol for the preparation of enantiopure (1S,2S,4R)-1,2-diol from (R)-limonene and (1R,2R,4S)-1,2-diol from (S)-limonene was developed.

Non-Isocyanate Polyurethane (NIPU) based on Rubber Seed Oil Synthesized via Low-Pressured Carbonization Reaction

Epoxidised rubber seed oil (ERSO) was successfully synthesized into non-isocyanate polyurethane via carboxylation method whereas peroxoformic acid was formed by in-situ reaction for epoxidation. The effects of temperature and ratio of hydrogen peroxide and formic acid to rubber seed oil carboxylation were studied. The optimum temperature for the epoxidation reaction was found at 50 °C to avoid ring opening reaction of epoxy whilst the optimum ratio of hydrogen peroxide and formic acid is equal molar of double bond: formic acid at 1:2 and 1:1, respectively. At a lower concentration of hydrogen peroxide and formic acid, the oxirane ring was stable due to the lower hydrolysis (oxirane cleavage) of an epoxide. The effect of using low content of formic acid tends to minimize unwanted epoxide ring opening to occur and make the epoxidation rate increased with increasing of oxirane number. Fourier transform infrared (FTIR) spectral displayed the presence of an epoxy functional group at 822 cm-1 and the disappearance of double bond peak at 3011 cm-1 corresponding to epoxidised oil and carbonyl group confirmed the epoxidation reaction had taken place. 1H-NMR was used to confirm the formation of carboxylate functionality after the reaction of epoxy at δ 4.83 and 4.61 ppm. In conclusion, ERSO has great potential to be used as a precursor in producing environmentally friendly non-isocyanate polyurethane.

Two (Chemo)-Enzymatic Cascades for the Production of Opposite Enantiomers of Chiral Azidoalcohols

Multi-step cascade reactions have gained increasing attention in the biocatalysis field in recent years. In particular, multi-enzymatic cascades can achieve high molecular complexity without workup of reaction intermediates thanks to the enzymes’ intrinsic selectivity; and where enzymes fall short, organo- or metal catalysts can further expand the range of possible synthetic routes. Here, we present two enantiocomplementary (chemo)-enzymatic cascades composed of either a styrene monooxygenase (StyAB) or the Shi epoxidation catalyst for enantioselective alkene epoxidation in the first step, coupled with a halohydrin dehalogenase (HHDH)-catalysed regioselective epoxide ring opening in the second step for the synthesis of chiral aliphatic non-terminal azidoalcohols. Through the controlled formation of two new stereocenters, corresponding azidoalcohol products could be obtained with high regioselectivity and excellent enantioselectivity (99% ee) in the StyAB-HHDH cascade, while product enantiomeric excesses in the Shi-HHDH cascade ranged between 56 and 61%.

Exploring tailor-made Brønsted acid sites in mesopores of tin oxide catalyst for β-alkoxy alcohol and amino alcohol syntheses

The generation of Brønsted (Sn–OH) and Lewis (coordinatively unsaturated metal centers) acidic sites on the solid surface is a prime demand for catalytic applications. Mesoporous materials are widely employed as catalysts and supports owing to their different nature of acidic sites. Nevertheless, the procedure adopted to generate acid functionalities in these materials involves tedious steps. Herein, we report the tunable acidic sites containing Brønsted sites with relatively varied acid strength in tin oxide by employing soft template followed by simple thermal treatment at various temperatures. The readily accessible active sites, specifically Brønsted acidic sites distributed throughout the tin oxide framework as well as mesoporosity endow them to perform with exceptionally high efficiency for epoxide ring opening reactions with excellent reusability. These features promoted them to surpass stannosilicate catalysts for the epoxide ring opening reactions with alcohol as a nucleophile and the study was extended to aminolysis of epoxide with the amine. The existence of relatively greater acid strength and numbers in T-SnO2-350 catalyst boosts to produce a high amount of desired products over other tin oxide catalysts. The active sites responsible in mesoporous tin oxide for epoxide alcoholysis were studied by poisoning the Brønsted acidic sites in the catalyst using 2,6-lutidine as a probe molecule.