Enantioselective Copper-Catalyzed Formal [2+1] and [4+1] Annulations of Diynes with Ketones via Carbonyl Ylides.

Carbonyl ylides have proven to be powerful synthons for the efficient construction of various valuable O-heterocycles, and the formation of carbonyl ylides by the reaction of metal carbenes with carbonyls has attracted increasing attention over the past decades. However, a catalyst-controlled highly enantioselective reaction of carbonyl ylides from metal carbenes is extremely challenging. Herein, we report a novel copper-catalyzed asymmetric formal [2+1] and [4+1] annulations of diynes with ketones via carbonyl ylides. Importantly, this protocol not only represents the first example of successful asymmetric epoxidation via carbonyl ylides, but also constitutes the first reaction of vinyl cations with carbonyl compounds. This method leads to the divergent, practical and atom-economical synthesis of a range of chiral oxiranes and dihydrofurans in moderate to excellent yields with generally excellent enantioselectivities and diastereoselectivities via remote-stereocontrol strategy.

Biobased polyelectrolyte multilayer-coated hollow mesoporous silica as a green flame retardant for epoxy resin.

Here, we describe a multifunctional biobased polyelectrolyte multilayer-coated hollow mesoporous silica (HM-SiO2@CS@PCL) as a green flame retardant through layer-by-layer assembly using hollow mesoporous silica (HM-SiO2), chitosan (CS) and phosphorylated cellulose (PCL). The electrostatic interactions deposited the CS/PCL coating on the surface of HM-SiO2. Subsequently, this multifunctional flame retardant was used to enhance thermal properties and flame retardancy of epoxy resin. The addition of HM-SiO2@CS@PCL to the epoxy resin thermally destabilized the epoxy resin composite, but generated a higher char yield. Furthermore, HM-SiO2 played a critical role and generated synergies with CS and PCL to improve fire safety of the epoxy resin due to the multiple flame retardancy elements (P, N and Si). This multi-element, synergistic, flame-retardant system resulted in a remarkable reduction (51%) of peak heat release rate and a considerable removal of flammable decomposed products. Additionally, the incorporation of HM-SiO2@CS@PCL can sustainably recycle the epoxy resin into high value-added hollow carbon spheres during combustion. Therefore, the HM-SiO2@CS@PCL system provides a practical possibility for preparing recyclable polymer materials with multi-functions and high performances.

Self-assembly fabrication of hollow mesoporous silica@Co-Al layered double hydroxide@graphene and application in toxic effluents elimination.

Here, we propose a self-assembly process to prepare hierarchical HM-SiO2@Co-Al LDH@graphene, with the purpose of combining their outstanding performance. Hollow mesoporous silica was first synthesized as the core, using a novel sonochemical method, followed by a controlled shell coating process and chemical reduction. As a result of the electrostatic potential difference among HM-SiO2, Co-Al LDH, and graphene oxide, the HM-SiO2 spheres were coated by Co-Al LDH and graphene. Subsequently, the HM-SiO2@Co-Al LDH@graphene spheres were introduced into an epoxy resin (EP) matrix for investigation of their toxic effluents capture and elimination effectiveness during combustion. The amount of toxic CO and volatile organic compounds from the epoxy resin decomposition significantly suppressed after incorporating the HM-SiO2@Co-Al LDH@graphene hybrids, implying a reduced toxicity.