Efficient synthesis of α-amino-vinylphosphine oxides from alkyl nitriles via manganese-catalyzed phosphinoenamination.

A protocol for the synthesis of α-amino-vinylphosphine oxides by phosphinoenamination reaction between alkyl nitriles and phosphine oxides was developed. The combination of Mn(OAc)2 as a Lewis acid and guanidine as a Lewis base was found to be an efficient catalytic system for this reaction. A series of alkyl nitriles and phosphine oxides are compatible with this conversion, furnishing the desired products in up to 95% yield under mild conditions. Furthermore, this method demonstrates the capability of gram-scale synthesis.

Visible-light-induced C(sp3)-C(sp3) bond formation via radical/radical cross-coupling.

Radical/radical cross-coupling remains challenging due to diffusion control issues. Herein, we report a visible-light-induced radical/radical cross-coupling reaction of quaternary ammonium salts and Hantzschs via C-N and C-C bond cleavage. The current synthetic approach furnishes 1,2-diphenylethanes in moderate to good yields and provides a method for the construction of the C(sp3)-C(sp3) bond.

Bromide ion promoted practical synthesis of phosphinothioates of sulfinic acid derivatives and H-phosphine oxides.

A feasible method for the synthesis of phosphinothioates from sulfinic acid derivatives and phosphine oxides is described. This reaction can be carried out in an open flask at room temperature and in an aqueous medium. The scope of the sulfinic acid derivatives is extensive, with a wide range of sulfinate esters, sulfinic acids, and sodium sulfinates compatible with these conditions, with good to excellent yields of phosphinothioates. In addition, a gram-scale synthesis with this reaction is achieved. A mechanism of this procedure was proposed.

An Electrochemical Method for Deborylative Hydroxylation of Arylboronic Acids under Metal-free Conditions.

An electrochemical method for the synthesis of (poly)phenols via deborylative hydroxylation of arylborons has been well established under metal-free conditions, whose practicability and advantage has been highlighted by the preparation of drug molecules and preformation of scalable transformation. Mechanistic studies have demonstrated that superoxide anion radical was involved in the conversion followed by the reaction with arylboronic acid substrate.

Nickel-Catalyzed 1,1-Dihydrophosphinylation of Nitriles with Phosphine Oxides.

Treatment of phosphine oxides with nitriles usually furnishes 1,2-dihydrophosphinylation products. Herein, we developed a nickel-catalyzed 1,1-dihydrophosphinylation of nitriles with phosphine oxides to access primary amines. This reaction proceeded smoothly under very mild conditions. A series of nitriles and phosphine oxides were compatible with this conversion, and the desired products were obtained in moderate to good yields.

Conversions of aryl carboxylic acids into aryl nitriles using multiple types of Cu-mediated decarboxylative cyanation under aerobic conditions.

Here, we used malononitrile or AMBN as a cyanating agent to develop efficient and practical protocols for Cu-mediated decarboxylative cyanations, under aerobic conditions, of aryl carboxylic acids bearing nitro and methoxyl substituents at the ortho position as well as of heteroaromatic carboxylic acids. These protocols involved economical methods to synthesize value-added aryl nitriles from simple and inexpensive raw materials. Further diversification of the 2-nitrobenzonitrile product was performed to highlight the practicality of the protocols.

Selective C-C bond cleavage of amides fused to 8-aminoquinoline controlled by a catalyst and an oxidant.

Herein, copper-catalyzed direct C-C bond cleavage of amides fused to 8-aminoquinoline as a directing group to form urea in the presence of amines and dioxygen is reported. Compared to the previous C-H aminations of amides via C-H activation, this reaction presents a catalyst and oxidant controlled C-C bond cleavage strategy that enables amidation through a radical process. CuBr/Ag2CO3/O2 shows the best catalytic result at 150 °C. A series of aryl and alkyl amides were compatible with this transformation. Notably, this method provided access to cyclohexanone, one of the most important industrial materials. The pathway of this reaction was investigated.

Molecular Packing-Controlled Mechanical-Induced Emission Enhancement of Tetraphenylethene-Functionalised Pyrazoline Derivatives.

Organic mechanofluorochromic (MFC) materials with mechanical-induced emission enhancement (MIEE) are scarce. Herein, Aggregation-induced emission (AIE)-active tetraphenylethene-functionalised pyrazoline derivatives with various non-conjugated substituent groups (Br, F, N,N-dimethylamino and cyano groups for TPEB, TPEF, TPEN and TPECN, respectively) were designed and synthesised. The fluorescence spectra of the compounds in the solid state were sensitive to mechanical stimuli and exhibited unique MFC properties. The solid fluorescence peaks of all compounds were red shifted, whereas the quantum yields of TPEB, TPEF and TPEN were increased and that of TPECN was slightly reduced after grinding. The MIEE mechanism was systematically investigated through structure-property relationship studies. The results showed that the pyrazoline ring of TPEB with MIEE property formed H-dimer aggregates with weak π-π stacking in the solid state. After grinding, the synergistic effects of conformational planarization and destructive π-π interactions induced the red shift of the fluorescence peak and the intensity enhanced. TPECN formed incompact J-aggregates with weak intermolecular interactions instead. The conformational planarization and increased intermolecular interactions induced by grinding led to the red-shifted peak and the slightly reduced intensity. These results clearly demonstrated that the translation of packing arrangements is an efficient method to design MIEE materials, which opens a new scope for designing unique MFC materials.

Pd-Catalyzed Decarboxylative Ortho-Halogenation of Aryl Carboxylic Acids with Sodium Halide NaX Using Carboxyl as a Traceless Directing Group.

A highly regioselective Pd-catalyzed carboxyl directed decarboxylative ortho-C-H halogenation of cheap o-nitrobenzoic acids with NaX (X = I, Br) under aerobic conditions has been established. The utility of the method has been demonstrated by the gram-scale reaction and derivatization of the product. Experimental results have confirmed Pd and Bi played critical roles in the transformation and indicated the transformation might proceed via 2-halo-6-nitrobenzoic acid derivative intermediate.

Two AIEE-active α-cyanostilbene derivatives containing BF2 unit for detecting explosive picric acid in aqueous medium.

Two novel α-cyanostilbene derivatives bearing triphenylamine and BF2 groups are synthesized (named TPE-B and TPE-BN). The fluorescent emissions of compounds TPE-B and TPE-BN are hypochromatically shifted and bathochromically shifted, respectively, with increasing polarity of the solvents, suggesting that the two compounds have characteristic polarity-dependent solvatochromic effects. Furthermore, they show obvious aggregation-induced emission enhancement (AIEE) phenomenon in THF/water mixture solutions. Meanwhile, compounds TPE-B and TPE-BN emit orange and yellow fluorescence in their solid states, respectively. Most significantly, in aqueous medium, compounds TPE-B and TPE-BN can selectively and sensitively detect picric acid (PA) among a number of nitroaromatic compounds, and their limits of detection (LOD) are calculated as 1.26 × 10-6 M and 1.51 × 10-6 M, respectively. The recognition mechanism for PA can be attributed to the photo-induced electron transfer (PET) process and this is supported by density functional theory (DFT) calculation. This research provides two novel compounds for the rational design of AIEE-active materials for sensing systems.

Selective Phosphoramidation and Phosphonation of Benzoxazoles via Sequence Control.

A selective phosphoramidation and phosphonation of benzoxazole was developed with trialkyl phosphites in the presence of iodine under mild conditions. In the reaction, the transformation completes in 10 min at room temperature and the substrates are well tolerant, as 2-substituted azoles could afford the quaternary carbon-centered products. Significantly, phosphites could be selectively introduced into the C- and N-positions of the benzoxazoles by controlling the addition sequence and the ratio of substrates.

Copper-Mediated Oxidative Functionalization of C(sp3)-H Bonds with Isoquinolines: Two-Step Synthesis of 5-Oxaprotoberberinones.

A copper-mediated oxidative functionalization of C(sp3)-H bonds with isoquinolines via a radical process without ligands was achieved. The present system exhibits a novel pathway for the preparation of N-alkyl (benzyl) isoquinolin-1(2H)-ones in moderate to high yields. In addition, this procedure provides a simple method to afford 5-oxaprotoberberinones and their derivatives in two steps.

Metal Bridging for Directing and Accelerating Electron Transfer as Exemplified by Harnessing the Reactivity of AIBN.

A new strategy for tuning the electron transfer between radicals and enolates has been developed. This method elicits the innate reactivity of AIBN with a copper catalyst and enables a cascade reaction with cinnamic acids. Electron paramagnetic resonance studies and control experiments indicate that the redox-active copper species not only activates the radical by coordination, but also serves as a bridge to bring the radical and nucleophile within close proximity to facilitate electron transfer. By exploiting possible combinations of redox-active metals and radical entities with suitable coordinating functional groups, this strategy should contribute to the development of a broad range of radical-based reactions.

Copper-mediated tandem reaction of ß-ketoesters/ketones with tertiary amines for the synthesis of 2,3-dihydrofurans.

A copper-mediated tandem reaction of ß-ketoesters/ketones with tertiary amines was achieved, which provides a simple and efficient approach to the synthesis of 2,3-dihydrofuran derivatives. In this tandem reaction, the tertiary amine not only offers the methylene moiety but also serves as the base.

Highly diastereo- and enantioselective tandem reaction toward functionalized pyrrolidines with multiple stereocenters.

An efficient asymmetric tandem dual Michael reaction that constructs three contiguous stereocenters in acyclic open-chain systems with very high enantioselectivity and diastereoselectivity has been developed. This protocol provides a reliable and rapid approach for synthesis of chiral pyrrolidines with multiple stereocenters.

Copper-catalyzed oxidative amination of benzoxazoles via C-H and C-N bond activation: a new strategy for using tertiary amines as nitrogen group sources.

An efficient and conceptually new method for oxidative amination of azoles with tertiary amines via copper-catalyzed C-H and C-N bond activation has been developed. This protocol can be performed in the absence of external base and only requires atmospheric oxygen as oxidant. The catalyst system is very simple and efficient, which opens a new way for using tertiary amines as nitrogen group sources for C-N bond formation reactions.

Palladium-catalyzed benzylic addition of 2-methyl azaarenes to N-sulfonyl aldimines via C-H bond activation.

An efficient protocol for the generation of amines by palladium-catalyzed nucleophilic benzylic addition of 2-methyl-substituted azaarenes to N-sulfonyl aldimines under neutral conditions via C-H bond activation has been developed. This reaction represents a very efficient methodology for the synthesis of heterocycle-containing amines and thus opens a new way to access amines through C-H bond activation.

Chiral Brønsted acid directed iron-catalyzed enantioselective Friedel-Crafts alkylation of indoles with beta-aryl alpha'-hydroxy enones.

A cooperative catalytic system established by the combination of an iron salt and a chiral Brønsted acid has proven to be effective in the asymmetric Friedel-Crafts alkylation of indoles with beta-aryl alpha'-hydroxy enones. Good to excellent yields and enatioselectivities were observed for a variety of alpha'-hydroxy enones and indoles, particularly for the beta-aryl alpha'-hydroxy enones bearing an electron-withdrawing group at the para position of the phenyl ring (up to 90 % yield and 91 % ee). The proton of the chiral Brønsted acid, the Lewis acid activation site, as well as the inherent basic site for the hydrogen-bonding interaction of the Brønsted acid are responsible for the high catalytic activities and enantioselectivities of the title reaction. A possible reaction mechanism was proposed. The key catalytic species in the catalytic system, the phosphate salt of Fe(III), which was thought to be responsible for the high activity and good enantioselectivity, was then confirmed by ESIMS studies.

Copper/silver-cocatalyzed Conia-ene reaction of linear beta-alkynic beta-ketoesters.

A novel and general copper/silver catalytic system has been developed for the Conia-ene intramolecular reaction of linear beta-alkynic beta-ketoesters. In the presence of (CuOTf)2.C6H6 and AgSbF6 (or AgOAc), a variety of the linear beta-alkynic beta-ketoesters selectively underwent the Conia-ene intramolecular reaction in moderate to good yields.