New alkylamides from the pericarps of Zanthoxylum schinifolium.

The pericarps of Zanthoxylum schinifolium Sieb. et Zucc were called "green huajiao", which were used as traditional folk medicine and popular seasoning in China. In this study, twenty-seven alkylamides, including a rare alkylamide containing two amide groups (1), an alkylamide with a furan ring (5), six new alkylamide analogues (2-4, 6-8), together with nineteen known alkylamides (9-27) were isolated from green huajiao. Their structures were elucidated by extensive spectroscopic analysis, including 1D, 2D NMR, HRESIMS, and UV spectra. Furthermore, compounds 5, 18, 21, and 22 exhibited weak protective activity for corticosterone-induced PC12 cells damage.

Synthesis of C-N Axially Chiral N-Arylbenzo[g]indoles via a Central-to-Axial Chirality Conversion Strategy.

Gold-catalyzed cascade cyclization of diynes for the synthesis of previously unexplored C-N axially chiral N-arylbenzo[g]indoles was described. The transformation was achieved via a central-to-axial chirality conversion strategy. The chiral conversion exhibited high efficiency. Besides single C-N chiral axis, N-arylbenzo[g]indoles bearing both C-N and C-C chiral axes were also afforded. The title compound derived monophosphine ligand was prepared and was evaluated in Pd-catalyzed asymmetric allylic substitutions, showing excellent chiral induction ability.

Synthesis of cis-(8b,14a)-hexahydro-14H-dibenzo[f,h]oxazolo[3,2-b]isoquinolin-14-ones via photo cascade reaction.

A concise method for the synthesis of cis-(8b,14a)-hexahydro-14H-dibenzo[f,h]oxazolo[3,2-b]isoquinolin-14-ones 2 via photo-induced 3-([1,1'-biphenyl]-2-yl)-1-(2-hydroxyethyl)pyridin-2(1H)-ones 1 was developed. Irradiation of 1 in the solution of toluene with a 313 nm UV light in the presence of HCl gave cis-(8b,14a)-9a-α-hexahydro-14H-dibenzo[f,h]oxazolo[3,2-b]isoquinoli n-14-ones and cis-(8b,14a)-9a-ß-hexahydro-14H-dibenzo[f,h]oxazolo[3,2-b]isoquinolin-14-ones 2 (2-α and 2-ß) in good yields. The protocol simultaneously constructs dearomatized phenanthrene ring and oxindolizidinones ring by photo cascade reaction to achieve high bonding efficiency and high atomic efficiency. Additionally, the antitumor activities of 2 was evaluated and compounds 2b-α, 2b-ß, 2j-ß and 2 k-α showed similar or better activity compared to the cisplatin against tumor cell lines of Leukemia HL-60, lung cancer A594, liver cancer SMMC-7721 and breast cancer MDA-MB-231.

Rearrangement of 2-(benzofuran-2-yl)-3-phenylpyridines via photoinduced 6π-electrocyclization.

By photoinduced 6π-electrocyclization of 2-(benzofuran-2-yl)-3-phenylpyridine derivatives 1, a method for the synthesis of trans-dihydrobenzo[f]quinolines 2, cis-dihydrobenzo[f]quinolines 3 and 8b-methyl-1,8b-dihydrobenzo[f]quinolines 4 was developed. Irradiation of 2-(benzofuran-2-yl)-3-phenylpyridine 1 in acetone-H2O (5 : 1, v/v) with a 313 nm UV lamp under an argon atmosphere at room temperature successfully yielded 2, which was further converted into 3 at elevated temperature (200 °C) in glycerol. However, irradiating 2-(3-methylbenzofuran-2-yl)-3-phenylpyridines 1 in CH2Cl2 with a 254 nm UV lamp gave 4 in good yields. The syntheses of 2, 3 and 4via the 6π-electrocyclization rearrangement of 1 not only offer high atom efficiency but also do not require transition metal catalysts or additives.

Cobalt-Catalysed Asymmetric Addition and Alkylation of Secondary Phosphine Oxides for the Synthesis of P-Stereogenic Compounds.

The catalytic asymmetric synthesis of P-chiral phosphorus compounds is an important way to construct P-chiral ligands. Herein, we report a new strategy that adopts the pyridinyl moiety as the coordinating group in the cobalt-catalysed asymmetric nucleophilic addition/alkylation of secondary phosphine oxides. A series of tertiary phosphine oxides were generated with up to 99 % yield and 99.5 % ee, and with broad functional-group tolerance. Mechanistic studies reveal that (R)-secondary phosphine oxides preferentially interact with the cobalt catalysts to produce P-stereogenic compounds.

Synthesis of 6-phenylbenzo[h]quinolines via photoinduced dehydrogenative annulation of (E)-2-phenyl-3-styrylpyridines.

A concise and environmentally friendly protocol was developed for the synthesis of 6-phenylbenzo[h]quinolines. 6-Phenylbenzo[h]quinolines were obtained in good yields via irradiation of (E)-2-phenyl-3-styrylpyridines with a 254 nm UV light (64 W) in EtOH under an argon atmosphere in the presence of TFA. The reaction is a dehydrogenative annulation reaction that proceeds through 6π-electrocyclization, a [1,5]-H shift, 1,3-enamine tautomerization, and elimination of a hydrogen molecule to afford 6-phenylbenzo[h]quinolines. The described protocol not only avoids the usage of a transition metal catalyst and an oxidant but also has the advantages of high atom efficiency and mild reaction conditions.

Synthesis of cis/trans-dihydrochromenones via a photoinduced rearrangement of 4-phenyl-3-aryl/cyclohexenylcoumarins.

A concise and environmentally friendly protocol has been developed for the synthesis of cis-dihydrochromenones and trans-dihydrochromenones in EtOH at room temperature. Irradiation of 4-phenyl-3-arylcoumarins in EtOH with 313 nm UV light under an argon atmosphere at room temperature gave cis-4b,15c-dihydro-16H-benzofuro[3',2':7,8]phenanthro[9,10-c]chromen-16-ones and cis-8c,14b-dihydro-9H-benzo[11,12]chryseno[5,6-c]chromen-9-ones in good yields. And an analogous treatment of 4-phenyl-3-alkenylcoumarins as 4-phenyl-3-arylcoumarins provided trans-1,2,3,4,4a,14b-hexahydro-5H-phenanthro[9,10-c]chromen-5-ones. The described photorearrangement proceeded smoothly without the addition of any transition metals and additives. The photorearrangement of 4-phenyl-3-arylcoumarins is believed to proceed via 6π-electrocyclization, a [1,3]-hydrogen shift and keto-enol isomerization.

Light-Promoted C-N Coupling of Aryl Halides with Nitroarenes.

A photochemical C-N coupling of aryl halides with nitroarenes is demonstrated for the first time. Catalyzed by a NiII complex in the absence of any external photosensitizer, readily available nitroarenes undergo coupling with a variety of aryl halides, providing a step-economic extension to the widely used Buchwald-Hartwig C-N coupling reaction. The method tolerates coupling partners with steric-congestion and functional groups sensitive to bases and nucleophiles. Mechanistic studies suggest that the reaction proceeds via the addition of an aryl radical, generated from a NiI /NiIII cycle, to a nitrosoarene intermediate.

Synthesis of 7-hydroxy-6H-naphtho[2,3-c]coumarin via a TsOH-mediated tandem reaction.

A concise and efficient method for the synthesis of 7-hydroxy-6H-naphtho[2,3-c]coumarin using available 1-(2-hydroxyphenyl)-2-phenylethanone and Meldrum's acid has been developed. This transformation involved a tandem aldol reaction/lactonization/Friedel-Crafts reaction to form a lactone ring and a benzene ring. It showed high atom economy with water and acetone as the byproducts. Mechanism studies demonstrated two roles of Meldrum's acid: (i) as the reagent for the tandem reaction, and (ii) as the catalyst for the Friedel-Crafts reaction. Moreover, the hydroxyl group of 7-hydroxy-6H-naphtho[2,3-c]coumarin was further functionalized efficiently by arylethynyl, aryl, and cyano groups to furnish D-π-A compounds with excellent fluorescence emissions (ΦF = 0.14-0.78).

Stereoselective Synthesis of (E)-3-Alkylideneoxindoles via Gold(I)-Catalyzed Cross-Coupling of 3-Diazooxindoles with Diazoesters.

A versatile gold(I)-catalyzed cross-coupling reaction of 3-diazooxindoles with diazoesters has been presented, affording (E)-3-alkylideneoxindoles stereoselectively. Density functional theory calculations rationalized the chemo- and stereoselectivity of the reaction, which was in good agreement with experimental observations. In addition, (E)-3-alkylideneoxindoles were converted into their (Z)-isomers under UV-irradiation facilely, indicating the great advantage of this approach in stereoselective synthesis of both (E)- and (Z)-3-alkylideneoxindoles.

π-Expanded Coumarins: One-Pot Photo Synthesis of 5H-Benzo[12,1]tetrapheno[7,6,5-cde]chromen-5-ones and Photophysical Properties.

The synthesis of a unique type of π-expanded coumarin derivatives, bearing six fused phenyl rings, was achieved via one-pot Suzuki reaction and visible light-driven electrocyclization. The large π-expanded 5H-benzo[12,1]tetrapheno[7,6,5-cde]chromen-5-ones were obtained in good to high yields from 1-bromo-2H-phenaleno[1,2,3-de]chromen-2-ones, and the intriguing optical properties were explored by altering the attached functional groups. 2-Arylaminosubstituted-5H-benzo[12,1]tetrapheno[7,6,5-cde]chromen-5-ones showed a large Stokes shift (4005 cm-1) or excellent fluorescence quantum yield (Φf = 0.75) along with significant bathochromic shift in tetrahydrofuran.

Metal-Free Synthesis of 3-(Iso)quinolinyl 4-Chromenones and 3-(Iso)quinolinyl 4-Quinolones from (Iso)quinoline N-Oxides and Ynones.

A general approach for the synthesis of 3-(iso)quinolinyl 4-chromenones and 3-(iso)quinolinyl 4-quinolones from (iso)quinoline N-oxides and ynones under metal-free conditions was developed. The reaction of (iso)quinoline N-oxide with the electron-deficient alkyne first generated an (iso)quinolinyl ß-diketone intermediate, which then underwent an intramolecular dehydration, affording 3-(iso)quinolinyl 4-chromenones and 3-(iso)quinolinyl 4-quinolones.

Syntheses of Benzofuranoquinolines and Analogues via Photoinduced Acceptorless Dehydrogenative Annulation of o-Phenylfuranylpyridines.

A strategy for the syntheses of benzofuranoquinolines and its analogues via the irradiation of o-phenylfuranyl/thienylpyridines/pyrimidines in DCM with UV light at rt under an argon atmosphere is described. The mechanism of this reaction through the process of 6π-electrocyclization, [1,5]-hydrogen shift, and 1,3-eneamine tautomerism leading to H2 evolution was elucidated. Notably, the syntheses of cis-8b-methyl-8b,13a-dihydrobenzo[f]benzofuro[3,2-h]quinolone via the photoinduced rearrangement of 2-(3-methylbenzofuran-2-yl)-3-phenylpyridine relevant to the mechanism of this reaction highlights the importance of the developed methodology.

Two-Step Synthesis of π-Expanded Maleimides from 3,4-Diphenylfuran-2(5H)-ones.

An efficient two-step synthesis of π-expanded maleimide derivatives was reported, which proceeded via a photoinduced dehydrogenative annulation of 3,4-diphenylfuran-2(5H)-ones in EtOH at room temperature for 5 h under an argon atmosphere, followed by interaction with primary amine in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene and O2. The synthesis of highly conjugated maleimides demonstrated that 3,4-diphenylfuran-2(5H)-ones were useful precursors for synthesis of π-expanded lactones and π-expanded maleimides with no need of a transition-metal catalyst. Additionally, the fluorescent properties of the highly conjugated maleimides were characterized and were found to possess high fluorescence quantum yields in dichloromethane solution.

Catalyst- and Additive-Free Cascade Reaction of Isoquinoline N-Oxides with Alkynones: An Approach to Benzoazepino[2,1-a]isoquinoline Derivatives.

A cascade reaction of isoquinoline N-oxides with alkynones was developed, delivering a fluorescent benzoazepino[2,1-a]isoquinoline derivative. The reaction worked smoothly without requirement of any catalyst or additive, making this method economical and easy to handle.

Synthesis of (2-hydroxyphenyl)(fusedphenyl)methanones via the photo-induced rearrangement of 2'-arylisoflavones.

The photo-induced rearrangement of 2'-arylisoflavones (aryl = phenyl, furyl, 3-pyridyl, 1-naphenyl, and 2-naphenyl) for the synthesis of (2-hydroxyphenyl)(fused phenyl)methanones in EtOH under an Ar atmosphere at room temperature has been developed. The described method proceeded smoothly without requiring any transition metal catalyst, oxidant, or additives. Moreover, using ethanol as the solvent is not only cost efficient but also environmentally friendly. Further treatment of methanone analogues with AlCl3 yielded highly conjugated polycyclic aromatic hydrocarbon (PAH) derivatives.

Synthesis of Polycyclic Heteroaromatic Coumarins via Photoinduced Dehydrogenative Annulation of 4-Phenyl-3-heteroarylcoumarins.

An efficient, oxidant and metal-free synthesis of polycyclic heteroaromatic coumarins was developed. H-Furo[2',3':3,4]naphtho[2,1-c]chromen-4-one (2a-2f), 1H-benzofuro[2',3':3,4]naphtho[2,1-c]chromen-1-one (2g-2j), and 4H-thieno[2',3':3,4]naphtho[2,1-c]chromen-4-one (2k-2s) derivatives were obtained by the irradiation of 4-phenyl-3-heteroarylcoumarin in EtOH-H2O (9:1, v/v) using a high-pressure Hg lamp as the light source, at room temperature and under an Ar atmosphere. Owing to the expansion of the π-conjugation system, 2a-2s showed strong fluorescence emissions in ethanol solution ( ΦF = 0.40-0.83).

One-pot synthesis of 3-fluoroflavones via 1-(2-hydroxyphenyl)-3-phenylpropane-1,3-diones and selectfluor at room temperature.

A concise and efficient one-pot strategy to synthesize 3-fluoroflavones was developed. 1-(2-Hydroxyphenyl)-3-phenylpropane-1,3-diones were fluorinated using selectfluor with a small amount of CH3CN at room temperature, followed by cyclization and dehydration in the presence of a trace amount of conc. H2SO4 to provide 3-fluoroflavones. The desired 3-fluoroflavone analogues were obtained in moderate to excellent yields. This strategy tolerated a wide range of functional groups and did not need sophisticated instruments or tedious substrate preparation.

Oxidant and Transition-Metal-Free Photoinduced Direct Oxidative Annulation of 1-Aryl-2-(furan/thiophen-2-yl)butane-1,3-diones.

A photoinduced direct oxidative annulation of 1-aryl-2-(furan/thiophen-2-yl)butane-1,3-diones and ethyl-2-(furan-2-yl)-3-oxo-3-(aryl-2-yl)propanoates in EtOH without the need for any transition metals and oxidants provided access to highly functionalized polyheterocyclic 1-(5-hydroxynaphtho[2,1-b]furan-4-yl)ethanones and 1-(5-hydroxyfuran/thieno/pyrrolo[3,2-e]benzofuran-4-yl)ethanones. The phenomenon of excited-state intramolecular proton transfer (ESIPT) was observed for both 1-(5-hydroxynaphtho[2,1-b]furan-4-yl)ethanone and 1-(5-hydroxy furan/thieno/pyrrolo[3,2-e]benzofuran-4-yl)ethanone analogues.