Catalytic Asymmetric Desymmetrization of Cyclic 1,3-Diketones Using Chiral Boro-phosphates.

Herein, we report a chiral boro-phosphate-catalyzed reductive amination for the desymmetrization of 2,2-disubstituted 1,3-cyclopentadiones with pinacolborane as the reducing agent, delivering chiral ß-amino ketones with an all-carbon quaternary stereocenter in good yields (≤94%), high enantioselectivities (≤97% ee), and excellent diastereoselectivities (>20:1 dr). This reaction has a broad substrate scope and high functional group tolerance. The importance of the chiral products was also demonstrated through the preparation of multifunctional building blocks and heterocycles.

Biodegradable and flame-retardant cellulose-based wearable triboelectric nanogenerator for mechanical energy harvesting in firefighting clothing.

Integrating flexible triboelectric nanogenerators (TENGs) into firefighting clothing offers exciting opportunities for wearable portable electronics in personal protective technology. However, it is still a grand challenge to produce eco-friendly TENGs from biodegradable and low-cost natural polymers for mechanical-energy harvesting and self-powered sensing. Herein, conductive polypyrrole (PPy) and natural chitosan (CS)/phytic acid (PA) tribonegative materials were employed onto the Lycra fabric (LC) in turn to assemble the biodegradable and flame-retardant single-electrode mode LC/PPy/CS/PA TENG (abbreviated as LPCP-TENG). The resultant LPCP-TENG exhibits truly wearable breathability (1378.6 mm/s), elasticity (breaking elongation 291 %), and shape adaptivity performance that can produce an open circuit voltage of 0.3 V with 2 N contact pressure at a working frequency of 5 Hz with a limiting oxygen index of 35.2 %. Furthermore, facile monitoring for human motion of firefighters on fireground is verified by LPCP-TENG when used as self-powered flexible tactile sensor. In addition, degradation experiments have shown that waste LPCP-TENG can be fully degraded in soil within 120 days. This work broadens the applicational range of wearable TENG to reduce the environmental effects of abandoned TENG, exhibiting prosperous applications prospects in the field of wearable power source and self-powered motion detection sensor for personal protection application on fireground.

Temperature-Arousing Self-Powered Fire Warning E-Textile Based on p-n Segment Coaxial Aerogel Fibers for Active Fire Protection in Firefighting Clothing.

Firefighting protective clothing is a crucial protective equipment for firefighters to minimize skin burn and ensure safety firefighting operation and rescue mission. A recent increasing concern is to develop self-powered fire warning materials that can be incorporated into the firefighting clothing to achieve active fire protection for firefighters before the protective clothing catches fire on fireground. However, it is still a challenge to facilely design and manufacture thermoelectric (TE) textile (TET)-based fire warning electronics with dynamic surface conformability and breathability. Here, we develop an alternate coaxial wet-spinning strategy to continuously produce alternating p/n-type TE aerogel fibers involving n-type Ti3C2Tx MXene and p-type MXene/SWCNT-COOH as core materials, and tough aramid nanofiber as protective shell, which simultaneously ensure the flexibility and high-efficiency TE power generation. With such alternating p/n-type TE fibers, TET-based self-powered fire warning sensors with high mechanical stability and wearability are successfully fabricated through stitching the alternating p-n segment TE fibers into aramid fabric. The results indicate that TET-based fire warning electronics containing 50 p-n pairs produce the open-circuit voltage of 7.5 mV with a power density of 119.79 nW cm-2 at a temperature difference of 300 °C. The output voltage signal is then calculated as corresponding surface temperature of firefighting clothing based on a linear relationship between TE voltage and temperature. The fire alarm response time and flame-retardant properties are further displayed. Such self-powered fire warning electronics are true textiles that offer breathability and compatibility with body movement, demonstrating their potential application in firefighting clothing.

Asymmetric Rubottom-Type Oxidation Catalyzed by Chiral Calcium Phosphates.

Invited for the cover of this issue is the group of Jon C. Antilla at Zhejiang Sci-Tech University. The image depicts asymmetric Rubottom-type oxidation catalyzed by chiral calcium phosphates. Read the full text of the article at 10.1002/chem.202203720.

Enantioselective Mukaiyama-Michael Reaction of ß,γ-Unsaturated α-Keto Esters with Silyl Ketene Acetals Catalyzed by a Chiral Magnesium Phosphate.

We would like to describe an efficient and highly enantioselective Mukaiyama-Michael reaction of silyl ketene acetals with ß,γ-unsaturated α-keto esters catalyzed by a chiral magnesium BINOL-derived phosphate. The resulting functionalized 1,5-dicarbonyl adducts are obtained in high yields (up to 96%) and with excellent enantioselectivities (up to 98%) under mild conditions. Two plausible mechanistic pathways were proposed, including a 1,4-addition and a hetero Diels-Alder [4 + 2] cycloaddition.

Asymmetric Rubottom-Type Oxidation Catalyzed by Chiral Calcium Phosphates.

A highly efficient catalytic asymmetric Rubottom-type oxidation is described. Using meta-chloroperbenzoic acid (m-CPBA) as the oxidant and chiral calcium phosphate as the catalyst, the facile transformation enables direct hydroxylation of N-Boc oxindoles and ß-ketoesters in high yields (up to 99 %) and in a highly enantioenriched fashion (up to >99 % ee). The application of the established method was demonstrated by the synthesis of a pharmaceutically important 3-hydroxyoxindole with excellent enantiocontrol.

Asymmetric Reductive Amination with Pinacolborane Catalyzed by Chiral SPINOL Borophosphates.

The catalytic asymmetric reductive amination of ketones with pinacolborane employing chiral SPINOL-derived borophosphates as catalysts has been realized. A series of chiral amine derivatives bearing multiple functional groups were obtained in good to excellent yields and enantioselectivities (up to 97% yield, 98% ee) under mild reaction conditions. Moreover, the synthetic applicability of the established method has been demonstrated by the asymmetric synthesis of (R)-Fendiline.

An Ultralight Self-Powered Fire Alarm e-Textile Based on Conductive Aerogel Fiber with Repeatable Temperature Monitoring Performance Used in Firefighting Clothing.

Firefighting protective clothing is an essential equipment that can protect firefighters from burn injuries during the firefighting process. However, it is still a challenge to detect the damage of firefighting protective clothing at an early stage when firefighters are exposed to excessively high temperature in fire cases. Herein, an ultralight self-powered fire alarm electronic textile (SFA e-textile) based on conductive aerogel fiber that comprises calcium alginate (CA), Fe3O4 nanoparticles (Fe3O4 NPs), and silver nanowires (Ag NWs) was developed, which achieved ultrasensitive temperature monitoring and energy harvesting in firefighting clothing. The resulting SFA e-textile was integrated into firefighting protective clothing to realize wide-range temperature sensing at 100-400 °C and repeatable fire warning capability, which could timely transmit an alarm signal to the wearer before the firefighting protective clothing malfunctioned in extreme fire environments. In addition, a self-powered fire self-rescue location system was further established based on the SFA e-textile that can help rescuers search and rescue trapped firefighters in fire cases. The power in the self-powered fire location system was offered by an SFA e-textile-based triboelectric nanogenerator (TENG). This work provided a useful design strategy for the preparation of ultralight wearable temperature-monitoring SFA e-textile used in firefighting protective clothing.

Ecofriendly flame-retardant composite aerogel derived from polysaccharide: Preparation, flammability, thermal kinetics, and mechanism.

Bio-based aerogel (polysaccharide cryogel) have led to a growing interest because of eco-friendliness, sustainability and excellent thermal insulation properties. Herein, we report an eco-friendly strategy to construct lightweight and porous sodium alginate/carboxymethyl cellulose/chitosan polysaccharide-based composite aerogels (SCC-B) by freeze-drying and post-cross-linking technology. The ester cross-linking of polysaccharide component achieved strong web-like entangled structure when using 1,2,3,4-butanetetracarboxylic acid and sodium hypophosphite as eco-friendly co-additives, meanwhile significantly improved flame retardancy of SCC-B due to phosphorylation. The thermal kinetic behavior of SCC-B was investigated by Flynn-Wall-Ozawa and Kissinger models. Results indicated that peak heat release rate and total heat release of SCC-B decreased from 30 W/g to 20 W/g and 15 kJ/g to 10 kJ/g, respectively. Furthermore, the second-degree burn time of SCC-B reached up to 87.1 s under heat exposure of 11.3 kW/m2. These characteristics combine to suggest hopeful prospects for use of SCC-B in the fields of fire-protection clothing as a renewable flame-retardant material.

Catalytic Asymmetric C-7 Friedel-Crafts Alkylation/N-Hemiacetalization of 4-Aminoindoles.

A unique catalytic asymmetric C-7 Friedel-Crafts alkylation/N-hemiacetalization cascade reaction of 4-aminoindoles with ß,γ-unsaturated α-keto esters has been described. Using a chiral magnesium H8-BINOL-derived bis(phosphate) complex as catalyst, the resulting functionalized 1,7-annulated indole scaffolds are obtained in high yields (up to 98%) and with good to excellent enantioselectivities (up to 99%) and diastereoselectivities (up to >20:1) under mild reaction conditions.

Catalytic Asymmetric Reduction of α-Trifluoromethylated Imines with Catecholborane by BINOL-Derived Boro-phosphates.

A catalytic enantioselective reduction of α-trifluoromethylated imines by a BINOL-derived boro-phosphate employing catecholborane as hydride source has been developed. This method provides an efficient route to prepare synthetically useful chiral α-trifluoromethylated amines in high yields and with excellent enantioselectivities (up to 98% yield and 96% ee) under mild conditions.

Flame-retardant PNIPAAm/sodium alginate/polyvinyl alcohol hydrogels used for fire-fighting application: Preparation and characteristic evaluations.

A novel fire-preventing triple-network (TN) hydrogel was prepared and laminated on cotton fabric to improve fire-resistant performance of cellulose fabric. The TN hydrogel composed of Poly (N-isopropylacrylamide) (PNIPAAm)/sodium alginate (SA)/ Poly (vinyl alcohol) (PVA) exhibited excellent swelling ratio, swelling-deswelling behavior and antibacterial property. Results indicated that introduction of SA could improve water retention capabilities of TN hydrogels. Thermogravimetric experiments showed that the thermal stability of hydrogels was best at a SA: PVA ratio of 2:1. Furthermore, the obtained hydrogel-cotton fabric laminates displayed efficient flame retardancy. Compared to original fabric, hydrogel-fabric laminates were nearly undamaged when exposed to fire for 12 s. This result is attributed to energy absorption as water is heated and evaporates in the hydrogel. The present work provides a new concept to prepare fire-resistant polymer fabric, which may be used in fire-protective clothing to protect the skin from burn injuries.

Facile synthesis of a novel transparent hyperbranched phosphorous/nitrogen-containing flame retardant and its application in reducing the fire hazard of epoxy resin.

In this study, a novel hyperbranched phosphorus/nitrogen-containing flame retardant (HPNFR) was facilely synthesized via the transesterification reaction of dimethyl methylphosphonate and tris (2-hydroxyethyl) isocyanurate and characterized successfully by 1H NMR and FTIR. The sample with 4 wt% HPNFR can achieve V-0 rating in UL-94 test and possess a LOI value as high as 34.5%. Conspicuous blowing-out effect was observed during the vertical burning test. TG results indicated that the presence of HPNFR significantly improved the thermal stability of EP thermosets. From cone test, THR, p-HRR, p-SPR and TSP values of HPNFR/EP composites were decreased in comparison to those of pure EP, revealing the reduced fire hazard of EP composites with HPNFR. SEM images of EP thermoset with 4 wt% of HPNFR after cone test exhibited compact and continuous char layers, while those of pure EP are fragmentary and broken. From TG-IR test, the yield of toxic CO and other pyrolysis products was significantly reduced, indicating a decrease in toxicity. Phosphorus-containing compounds were detected in gas phase, which verified the gaseous phase flame retardant effect of HPNFR. Besides, HPNFR would not significantly damage the transparence of EP thermosets, consequently reserved it's application value in some special fields.

Design and synthesis of new alkyl-based chiral phosphoric acid catalysts.

Using chiral BINOL-derived phosphoric acids (PA's) to activate substrates for enhanced reactivity is now regarded as a powerful strategy to control enantioselectivity in asymmetric synthesis. Generally, most substituents at the 3,3'-positions of BINOL PA's are aryl derivatives. These derivatives are pivotal in attaining high selectivity. PA's with alkyl substituents in these positions have rarely been reported. Herein, we introduced alkyl-based substituents at the 3,3'-position of PA's. These new potential catalysts, if applied in reactions, may allow altered noncovalent interactions (as opposed to the typical aryl substituents in these positions) with substrates used in chiral PA-catalyzed chemistry in the future.