Metal-Free Aminophosphonation: Eco-friendly Synthesis and Photophysical Properties of Fluorescent 3-(Aminoimidazo[1,2-a]pyridin-2-yl)phosphonates.

We report a novel, metal-free procedure for the direct aminophosphonation of imidazo[1,2-a]pyridines in green solvents under open air conditions. This method is characterized by its mild and sustainable conditions, ease of operation, scalability, and excellent functional group compatibility. The synthesized compounds exhibit promising photophysical properties, including significant Stokes shifts and quantum yields, making them potential candidates for innovative fluorescent probes.

Catalytic Formal [2π+2σ] Cycloaddition of Aldehydes with Bicyclobutanes: Expedient Access to Polysubstituted 2-Oxabicyclo[2.1.1]hexanes.

Synthesis of bicyclic scaffolds has attracted tremendous attention because they are playing an important role as saturated bioisosteres of benzenoids in modern drug discovery. Here, we report a BF3 -catalyzed [2π+2σ] cycloaddition of aldehydes with bicyclo[1.1.0]butanes (BCBs) to access polysubstituted 2-oxabicyclo[2.1.1]hexanes. A new kind of BCB containing an acyl pyrazole group was invented, which not only significantly facilitates the reactions, but can also serve as a handle for diverse downstream transformations. Furthermore, aryl and vinyl epoxides can also be utilized as substrates which undergo cycloaddition with BCBs after in situ rearrangement to aldehydes. We anticipate that our results will promote access to challenging sp3 -rich bicyclic frameworks and the exploration of BCB-based cycloaddition chemistry.

Diboron(4)-Catalyzed Remote [3+2] Cycloaddition of Cyclopropanes via Dearomative/Rearomative Radical Transmission through Pyridine.

Ring structures such as pyridine, cyclopentane or their combinations are important motifs in bioactive molecules. In contrast to previous cycloaddition reactions that necessitated a directly bonded initiating functional group, this work demonstrated a novel through-(hetero)arene radical transmission concept for selective activation of a remote bond. An efficient, metal-free and atom-economical [3+2] cycloaddition between 4-pyridinyl cyclopropanes and alkenes or alkynes has been developed for modular synthesis of pyridine-substituted cyclopentanes, cyclopentenes and bicyclo[2.1.1]hexanes that are difficult to access using known methods. This complexity-building reaction was catalyzed by a very simple and inexpensive diboron(4) compound and took place via dearomative/rearomative processes. The substrate scope was broad and more than 100 new compounds were prepared in generally high yields. Mechanistic experiments and density function theory (DFT) investigation supported a radical relay catalytic cycle involving alkylidene dihydropyridine radical intermediates and boronyl radical transfer.

One-Pot Sequence-Controlled Synthesis of Oligosiloxanes.

Silicones (organopolysiloxanes) have found applications in a wide range of research areas, and their unique and valuable properties have rendered these materials virtually irreplaceable. Despite the fact that silicones have been employed industrially for more than 70 years, synthetic routes to generate silicones remain limited, and the sequence-controlled synthesis of oligo- and polysiloxanes still represents a major challenge in silicone chemistry. Described here is a highly selective sequence-controlled synthesis of linear, branched, and cyclic oligosiloxanes by simple iteration of two reactions, specifically, a B(C6 F5 )3 -catalyzed dehydrocarbonative cross-coupling of alkoxysilanes with hydrosilanes and a B(C6 F5 )3 -catalyzed hydrosilylation of carbonyl compounds, in a single flask. The sequence of the resulting oligosiloxanes can be controlled precisely by the order of addition of the hydrosilane monomers.

High-Modulus Low-Cost Carbon Fibers from Polyethylene Enabled by Boron Catalyzed Graphitization.

Currently, carbon fibers (CFs) from the solution spinning, air oxidation, and carbonization of polyacrylonitrile impose a lower price limit of ≈$10 per lb, limiting the growth in industrial and automotive markets. Polyethylene is a promising precursor to enable a high-volume industrial grade CF as it is low cost, melt spinnable and has high carbon content. However, sulfonated polyethylene (SPE)-derived CFs have thus far fallen short of the 200 GPa tensile modulus threshold for industrial applicability. Here, a graphitization process is presented catalyzed by the addition of boron that produces carbon fiber with >400 GPa tensile modulus at 2400 °C. Wide angle X-ray diffraction collected during carbonization reveals that the presence of boron reduces the onset of graphitization by nearly 400 °C, beginning around 1200 °C. The B-doped SPE-CFs herein attain 200 GPa tensile modulus and 2.4 GPa tensile strength at the practical carbonization temperature of 1800 °C.

By-Product-Free Siloxane-Bond Formation and Programmed One-Pot Oligosiloxane Synthesis.

Siloxane bonds are usually synthesized by condensation reactions, such as hydrolysis/dehydration and cross-coupling reactions, in which the generation of by-products during bond formation can not be avoided. We have developed a one-pot sequence of iridium-catalyzed silyl ester hydrosilylation and boron-catalyzed rearrangement of the resulting disilyl acetals for the construction of siloxane bonds, in principle without the formation of any by-products. Moreover, the programmed synthesis of tri-, tetra-, and pentasiloxanes was possible in a single flask by combining the above sequence of iridium-catalyzed hydrosilylation and boron-catalyzed rearrangement with a boron-catalyzed cross-coupling reaction. The obtained oligosiloxanes are difficult to synthesize selectively by other known synthetic procedures.

(C6 F5 )3 B Catalyzed Chemoselective and ortho-Selective Substitution of Phenols with α-Aryl α-Diazoesters.

The development of an efficient method for the site-selective substitution of unprotected phenols has long been considered as an attractive but challenging task. Herein, we describe a highly chemo- and ortho-selective substitution reaction of phenols with α-aryl α-diazoacetates with commercially available (C6 F5 )3 B as the catalyst. This reaction proceeds under simple and mild conditions with high efficiency, it features a wide substrate scope and can be easily scaled up.

Iron boride boosted Fenton oxidation: Boron species induced sustainable FeIII/FeII redox couple.

The regeneration of Fe(II) is the rate-limiting step in the Fenton/Fenton-like chain reactions that seriously hinder their scientific progress towards practical application. In this study, we proposed iron boride (FeB) for the first time as a new material to sustainably decompose H2O2 to generate hydroxyl radicals, which can non-selectively degrade a wide array of refractory organic pollutants. Fe(II) can be steadily released by the stepwise oxidation of FeB to stimulate Fenton reaction, meanwhile, B-B bonds as electron donors on the surface of FeB effectively promote the regeneration of Fe(II) from Fe(III) species and significantly accelerate the production of hydroxyl radicals. The low generation of toxic by-products and the high utilization rate of iron species validly avoid the secondary organic/metal pollution in the FeB/H2O2 system. Therefore, FeB mediated Fenton oxidation provides a novel strategy to realize a green and long-lasting environmental remediation.