Net-1,2-Hydrogen Atom Transfer of Amidyl Radicals: Toward the Synthesis of 1,2-Diamine Derivatives.

Hydrogen atom transfer (HAT) processes are among the most useful approaches for the selective construction of C(sp3)-C(sp3) bonds. 1,5-HAT with heteroatom-centered radicals (O•, N•) have been well established and are favored relative to other 1,n-HAT processes. In comparison, net 1,2-HAT processes have been observed infrequently. Herein, the first amidyl radicalls are reported that preferentially undergo a net 1,2-HAT over 1,5-HAT. Beginning with single electron transfer from 2-azaallyl anions to N-alkyl N-aryloxy amides, the latter generate amidyl radicals. The amidyl radical undergoes a net-1,2-HAT to generate a C-centered radical that participates in an intermolecular radical-radical coupling with the 2-azaallyl radical to generate 1,2-diamine derivatives. Mechanistic and EPR experiments point to radical intermediates. Density functional theory calculations provide support for a base-assisted, stepwise-1,2-HAT process. It is proposed that the generation of amidyl radicals under basic conditions can be greatly expanded to access α-amino C-centered radicals that will serve as valuable synthetic intermediates.

Perylenediimide-Based Hybrid Materials for the Iodoperfluoroalkylation of Alkenes and Oxidative Coupling of Amines: Bay-Substituent-Mediated Photocatalytic Activity.

Inorganic-organic donor-acceptor hybrid compounds are an emerging class of multifunctional crystalline materials with well-defined structures built from semiconductive inorganic and organic components. Perylenediimides (PDIs) are a prominent class of electron-deficient organic dyes, which can undergo consecutive photoinduced electron transfers to generate doublet excited-state radical anions for photoredox-inert chemical bonds. Thus, this is an excellent organic component for building hybrid materials to study the structure-property relationships in organic synthesis. In this context, three molecular structure modified PDI-based hybrid materials, (Me4-PDI)2·SiW12O40 (1), (Me4-Cl4-PDI)2·SiW12O40 (2), and (Me4-Br2-PDI)1.5·HSiW12O40 (3), were studied. By the introduction of different substituent groups at the bay positions, these three hybrid materials were successfully fabricated to investigate the impact of substituent groups on the photocatalytic activity. As expected, all PDI-based hybrid materials easily underwent consecutive photoexcitation to obtain their excited-state radical anions. However, experimental and theoretical analyses showed that these obtained excited-state radical anions displayed unusual bay-substituent-group-dependent photocatalytic conversion activities for the iodoperfluoroalkylation of alkenes and oxidative coupling of amines. Higher conversion yields were obtained for complexes 1 and 3 (bay-unsubstituted and Br-substituted PDI hybrid materials, respectively), and lower conversion was observed for complex 2 (Cl-substituted PDI hybrid material), which is attributed to the excited-state SOMO-1 energies of the PDI radical anions. The structure-property relationship established in this work provides insights for the further exploration of bay-substituted PDI hybrid materials in other small-molecule photocatalytic transformations.

Synthesis and antitumor activity of novel hybrid compounds between 1,4-benzodioxane and imidazolium salts.

A series of novel hybrid compounds between 1,4-benzodioxane and imidazolium salts was designed and prepared. The compounds were evaluated in vitro against a panel of human tumor cell lines (K562, SMMC-7721, and A-549). The structure-activity relationship results demonstrated that the 2-methyl-benzimidazole or 5,6-dimethyl-benzimidazole ring and substitution of the imidazolyl-3-position with a 4-phenylphenacyl substituent were critical for promoting cytotoxic activity. Particularly, compound 25 was found to be the most potent compound with IC50 values of 1.06-8.31 µM against the three human tumor cell lines and exhibited higher selectivity to K562 and SMMC-7721 cells with IC50 values 4.5- and 4.7-fold lower than cisplatin. Moreover, compound 25 inhibited cell proliferation by inducing the G0/G1 cell cycle arrest and apoptosis in SMMC-7721 cells.

An electron-deficient MOF as an efficient electron-transfer catalyst for selective oxidative carbon-carbon coupling of 2,6-di-tert-butylphenol.

Naphthalene diimides (NDIs), a type of electron-deficient dye molecule with high quadrupole moment and excellent redox activity, have been utilized in various fields, such as energy transfer, chemical sensing, anion transport, and photo-/electrochromic materials. In this study, an electron-deficient metal-organic framework with one-dimensional channels, Eu2(BBNDI)3(DMF)2 (MOF 1) (H2BBNDI = N,N'-bis(3-benzoic acid)naphthalene diimide), was successfully constructed based on the naphthalene diimide derivative. Because of the generation of NDI radicals by electron transfer between components, this material exhibits fast-responsive reversible photochromic properties. Moreover, it shows high efficiency and selective oxidation of 2,6-di-tert-butylphenol to its quinone derivative, aldehyde, and dimeric or trimeric phenol derivative by controlling the reaction conditions.

Merging of the photocatalyst decatungstate and naphthalene diimide in a hybrid structure for the oxidative coupling of amines.

Designing and developing novel hybrid materials for the effective photoconversion of organic substrates is of great importance. Crystalline hybrid heterostructures, as an attractive class of material, are composed of semiconducting organic and inorganic components with fast-responsive charge-separated properties and thus they are promising photocatalysts. Naphthalene diimides (NDIs) and decatungstate (W10O324-) are two versatile semiconductor components that have been utilized as building blocks for the construction of functional materials for various applications. In this context, we demonstrated that the combination of an electron-deficient NDI derivative with W10O324- resulted in an organic-inorganic hybrid compound, namely Zn2(DPNDI)(W10O32)(DMA)6 (DPNDI = N,N'-di-(4-pyridyl)-1,4,5,8-naphthalene diimide) (1). Because of consecutive photo-induced electron transfer processes among the components, this hybrid compound exhibits fast-responsive reversible photochromic properties, and it efficiently photocatalytically oxidizes amines to imines under mild conditions with high yields and an excellent substrate application range.

Cylindrical metal liner implosion at extremes of pressure and material velocity on an intense pulsed power facility-FP-2.

Highly precise and controllable liner implosions driven by a pulsed power facility have extensive applications in exploration of advanced hydrodynamics at the extremes of pressure and material velocity. In this paper, we describe a new pulsed power facility developed in China named FP-2 (a series of facilities for Fluid Physics investigations-the second generation) for liner implosions. Benefiting from the reliable and stable operation of 48 rail gap switches, the FP-2 facility can steadily transmit a current of 10.5 MA to a dummy load of 10 nH in the case of a charging voltage of ±40 kV. The first quarter cycle is 5.5 µs, and the percentage shot-to-shot deviation of the current history is less than 1%. When the aluminum liners of 60 mm in height and 0.6 mm in thickness are adopted, the maximum velocity of 4.5 and 7.5 km/s has been achieved with the liner diameter of 90 and 60 mm, respectively, at the diameter of 10 mm. Experimental results show that the percentage shot-to-shot deviation of the liner velocity history is less than 1%. As impact on the target, the maximum of the impact time deviation measured from four perpendicular fiber pins is less than 20 ns. Due to the modular design of FP-2, it is convenient for a future upgrade. The confirmation of high-quality implosion on FP-2, such as high repeatability, high reliability, and high symmetry, makes it a bright prospect to explore the advanced hydrodynamic problems at extremes of pressure and material velocity in the future.

Aryl acrylonitriles synthesis enabled by palladium-catalyzed α-alkenylation of arylacetonitriles with vinyl halides/triflates.

Aryl acrylonitriles are an important subclass of acrylonitriles in the medicinal chemistry and pharmaceutical industry. Herein, an efficient synthesis of aryl acrylonitrile derivatives using a Palladium/NIXANTPHOS-based catalyst system was developed. This approach furnishes a variety of substituted and functionalized aryl acrylonitriles (up to 95% yield). The scalability of the transformation and the synthetic versatility of aryl acrylonitrile were demonstrated.

Nickel-catalyzed enantioselective vinylation of aryl 2-azaallyl anions.

A unique enantioselective nickel-catalyzed vinylation of 2-azaallyl anions is advanced for the first time. This method affords diverse vinyl aryl methyl amines with high enantioselectivities, which are frequently occurring scaffolds in natural products and medications. This C-H functionalization method can also be extended to the synthesis of enantioenriched 1,3-diamine derivatives by employing suitably elaborated vinyl bromides. Key to the success of this process is the identification of a Ni/chiraphos catalyst system and a less reducing 2-azaallyl anion, all of which favor an anionic vinylation route over a background radical reaction. A telescoped gram scale synthesis and a product derivatization study confirmed the scalability and synthetic potential of this method.

Transition-Metal-Free C(sp3)-H Coupling of Cycloalkanes Enabled by Single-Electron Transfer and Hydrogen Atom Transfer.

Here we report a unique transition-metal-free C(sp3)-H/C(sp3)-H coupling of cycloalkanes at room temperature. Unactivated cycloalkanes and 2-azaallyls underwent the combination process of single-electron transfer (SET) and hydrogen atom transfer (HAT) to deliver a wide variety of cycloalkane-functionalized products. This expedient approach enables C(sp3)-H/C(sp3)-H coupling of cycloalkanes under mild conditions without transition metals, initiators, and oxidants.

Metal-Free Synthesis of Phenol-Aryl Selenides via Dehydrogenative C-Se Coupling of Aryl Selenoxides with Phenols.

Herein, we disclose the synthesis of diaryl selenides through an unexpected C-Se coupling between aryl benzyl selenoxides and phenols. The synthetic significance of the method is that it provides a mild, rapid, and metal-free access to organoselenides in high yields with excellent functional group tolerance. This coupling of aryl benzyl selenoxides reveals a completely new reaction possibility compared with aryl sulfoxides. We also probed the reaction mechanism of this unexpected transformation through experimental studies and revealed a special Se(IV)-Se(III)-Se(II) reaction pathway.

Transition-metal-free C(sp3)-H/C(sp3)-H dehydrogenative coupling of saturated heterocycles with N-benzyl imines.

A unique C(sp3)-H/C(sp3)-H dehydrocoupling of N-benzylimines with saturated heterocycles is described. Using super electron donor (SED) 2-azaallyl anions and aryl iodides as electron acceptors, single-electron-transfer (SET) generates an aryl radical. Hydrogen atom transfer (HAT) from saturated heterocycles or toluenes to the aryl radical generates alkyl radicals or benzylic radicals, respectively. The newly formed alkyl radicals and benzylic radicals couple with the 2-azaallyl radicals with formation of new C-C bonds. Experimental evidence supports the key hydrogen-abstraction by the aryl radical, which determines the chemoselectivity of the radical-radical coupling reaction. It is noteworthy that this procedure avoids the use of traditional strong oxidants and transition metals.

Synthesis of Benzofuran Derivatives through Cascade Radical Cyclization/Intermolecular Coupling of 2-Azaallyls.

Benzofurans are among the most popular structural units in bioactive natural products, however, the synthesis of such structures by radical cyclization cascade reactions is rare. Herein, we report a mild and broadly applicable method for the construction of complex benzofurylethylamine derivatives through a unique radical cyclization cascade mechanism. Single-electron transfer (SET) from 2-azaallyl anions to 2-iodo aryl allenyl ethers initiates a radical cyclization that is followed by intermolecular radical-radical coupling. This expedient approach enables the synthesis of a range of polycyclic benzofurans that would otherwise be difficult to prepare.

Synthesis and cytotoxic activity of novel tetrahydrobenzodifuran-imidazolium salt derivatives.

The synthesis of a series of novel 4-substituted 2,3,6,7-tetrahydrobenzo [1,2-b;4,5-b']difuran-1H-imidazolium salts is presented. The biological properties of the compounds were evaluated in vitro against a panel of human tumor cell lines. Results suggest that the 5,6-dimethyl-benzimidazole or 2-methyl-benzimidazole ring, and substitution of the imidazolyl-3-position with a 2-naphthylmethyl substituent or 2-naphthylacyl substituent, were important to the cytotoxic activity. Notably, 3-(2-Naphthylmethyl)-1-((2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b']difuran-4-yl)methyl)-1H-5,6-dimethyl-benzimidazol-3-ium bromide (42) was found to be the most potent derivative against five human tumor cell lines with IC50 values of 1.06-4.34µM and more selective towards SMMC-7721, A549 and SW480 cell lines. 3-(2-Naphthylacyl)-1-((2,3,6,7-tetrahydrobenzo[1,2-b;4,5-b']difuran-4-yl)methyl)-1H-2-methyl-benzimidazol-3-ium bromide (37) showed higher selectivity to SMMC-7721 and MCF-7 cell lines with IC50 values 2.7-fold and 8.4-fold lower than DDP. Study regarding to the antitumor mechanism of action showed that compound 37 could induce cell cycle G1 phase arrest and apoptosis in SMMC-7721 cells.

Synthesis and antitumor activity of novel N-substituted tetrahydro-ß-carboline-imidazolium salt derivatives.

The synthesis of a series of novel N-substituted tetrahydro-ß-carboline-imidazolium salt derivatives is presented. The biological properties of the compounds were evaluated in vitro against a panel of human tumor cell lines. The results suggest that the benzimidazole ring and 1-(naphthalen-2-yl)ethan-1-one or 2-naphthylmethyl substituent at the imidazolyl-3-position were vital for modulating cytotoxic activity. Compound 41 was observed as a potent derivative with IC50 values of 3.24-8.78 µM and exhibited cytotoxic activity selectively against HL-60, A-549 and MCF-7 cell lines. Meanwhile, high inhibitory activities selectively against HL-60 and MCF-7 cell lines were observed for compound 51. Moreover, compound 51 was able to induce G1 phase cell cycle arrest and apoptosis in MCF-7 cells. The cytotoxicity of compound 51 against human normal lung epithelial cell line BEAS-2B was further evaluated.