Phosphine-catalyzed Rauhut-Currier reaction of γ-alkyl allenoate and subsequent trapping using the Diels-Alder reaction.

We have disclosed a Rauhut-Currier reaction of γ-alkyl-substituted allenoate, catalyzed by L-valine-derived amide phosphine, to form trisubstitued allenoate, which was trapped by maleimide or DMAD via the Diels-Alder reaction. Exo-bicyclic succinimide derivatives including three continuous stereocenters with an exo-carbon-carbon double bound were constructed in up to quantitative yields with high stereospecificity.

Palladium/Silver Cocatalyzed Divergent Dimerization of 2H-Azirines for Regioselective Synthesis of Tetrasubstituted Pyrroles and Pyrimidines.

The unprecedented dimerizations of 2H-azirines have been developed under the catalysis of palladium and silver. Upon changing the reaction conditions, the fully aryl-substituted pyrrole and pyrimidine derivatives were furnished in moderate yields with regiospecificity, respectively. Control experiments uncovered distinct catalytic effects of two transition metals, and the proposed catalytic cycles plausibly rationalized the chemodivergence and regioselectivity.

Synthesis of 3,4,5-trisubstituted phenols via Rh(III)-catalyzed alkenyl C-H activation assisted by phosphonium cations.

An efficient method for the construction of various 3,4,5-trisubstituted phenol derivatives has been achieved via the Rh(III)-catalyzed coupling of phosphonium cations with internal alkynes. This protocol shows good substrate compatibility, as an array of structurally and electronically diverse phosphonium compounds react efficiently with up to 87% yield.

Modular Synthesis of Tetrasubstituted Pyrroles via an Annulative Migration Reaction of Allenyl Ketones and p-Toluenesulfonylmethyl Isocyanide.

The metal-free cyclization of allenyl ketones and p-toluenesulfonylmethyl isocyanide (TosMIC), promoted by Cs2CO3, provides a convenient access to tetrasubstituted pyrroles in which an acyl group undergoes 1,2-migration. This tandem Michael addition/annulative migration synthetic strategy is general and high-yielding for various substituted allenyl ketones. Moreover, a phosphoryl or ester moiety is also a suitable functionality to enable such migration.

Regioselective intramolecular cyclization of o-alkynyl arylamines with the in situ formation of ArXCl to construct poly-functionalized 3-selenylindoles.

In this article, a practical and metal-free method for the synthesis of poly-functionalized 3-selenyl/sulfenyl/telluriumindoles from o-alkynyl arylamines has been achieved. In this protocol, the in situ formation of selenenyl chloride, sulfenyl chloride or tellurenyl chloride is considered as the key intermediate and the 3-selenyl/sulfenyl/telluriumindoles can be obtained in good to excellent yields. Furthermore, the product 2-phenyl-3-(phenylselanyl)-1-tosyl-1H-indole can be selectively oxidized to compounds 2-phenyl-3-(phenylseleninyl)-1-tosyl-1H-indole and 2-phenyl-3-(phenylselenonyl)-1-tosyl-1H-indole in good yields.

Rh(III)-catalyzed [4 + 1] cyclization of aryl substituted pyrazoles with cyclopropanols via C-H activation.

A rhodium-catalyzed formal [4 + 1]-cyclization reaction of aryl substituted pyrazoles with cyclopropanols via C-H bond activation/cyclization processes to selectively construct a series of carbonyl functionalized pyrazolo[5,1-a]isoindoles is described. The reaction features good functional group compatibility and a broad substrate scope with respect to both cyclization components with up to 84% yields. Mechanistic studies indicated that the C-H cleavage might be the rate-determining step in this transformation.

Rhodium(III)-Catalyzed Sequential Cyclization of N-Boc Hydrazones with Propargylic Monofluoroalkynes via C-H Activation/C-F Cleavage for the Synthesis of Spiro[cyclobutane-1,9'-indeno[1,2-a]indenes].

An effective rhodium(III) catalysis for the construction of valuable tetracyclic compounds is described herein. This domino process involving the C-H activation/[3 + 2] annulation/intramolecular Friedel-Crafts reaction sequences of simple and readily available N-Boc hydrazones and propargylic monofluoroalkynes afforded fused tetracyclic spiro[cyclobutane-1,9'-indeno[1,2-a]indenes] in moderate to good yields, featuring three C-C bond formation. Moreover, control experiments indicated that the C-H activation might be involved in the rate-determining step.

Synthesis of Trisubstituted Furans via Copper(I)-Catalyzed Strain-Driving Cycloisomerization/Annulative Fragmentation.

The in situ formed furan-fused cyclobutenes via Cu(I)-catalyzed cycloisomerization of readily available allenyl ketones bearing a cyclopropyl moiety are a highly reactive and powerful species, which undergo annulative fragmentation with terminal ynones to afford a wide variety of functional furans in moderate to high yields. This ring-distortion protocol features an unprecedented strain-controlled cycloisomerization/Diels-Alder/retro-Diels-Alder (CDRD) sequence under mild conditions.

Different functional groups modified porous organic polymers used for low concentration CO2 fixation.

Through a facile post-synthetic method, different kinds of polar group-functionalized ionic liquid porous organic polymers (POP-PA-COOH, POP-PA-OH, and POP-PA-NH2) were obtained. The materials can be used as efficient heterogeneous catalysts in the cycloaddition reaction of CO2 with epoxides under mild and co-catalyst-free conditions. It is demonstrated that POP-PA-NH2 possesses much higher catalytic activity than POP-PA-OH and POP-PA-COOH. Interestingly, this activity difference can further be amplified when the reaction is carried out under low CO2 concentration, and POP-PA-NH2 possesses a conversion of 84.7% with a selectivity of 99.0% in 96 h. It is noteworthy to mention that research focusing on the transformation of CO2 under low concentration using heterogeneous catalysts is rare and still a challenge. The excellent activities of POP-PA-NH2 under low CO2 concentration make this material a good candidate for CO2 elimination under mild conditions.

Enantioselective Phosphine-Catalyzed Trimerization of γ-Aryl-3-butynoates via Isomerization/[3 + 2] Cyclization/Michael Addition Cascade.

We disclose an l-isoleucine-derived amide phosphine-catalyzed trimerization of γ-aryl-3-butynoates, which undergo an isomerization to allenoate, [3 + 2] cyclization, and Michael addition cascade. Exocyclopentene derivatives bearing an all-carbon quaternary stereocenter were constructed stereospecifically and enantioselectively. A wide variety of γ-aryl-3-butynoates could be employed to deliver optically pure cyclopentene derivatives in moderate to good yields with ee values of ≥95% and in most cases ≥98%.

Optimization of the flow conditions in the spawning ground of the Chinese sturgeon (Acipenser sinensis) through Gezhouba Dam generating units.

Chinese sturgeon (Acipenser sinensis) is a critically endangered species, and waters downstream from Gezhouba Dam are the only known spawning ground. To optimize the velocity conditions in the spawning ground by controlling the opening mode of Gezhouba Dam generator units, a mathematical model of Chinese sturgeon spawning ground was established in FLOW-3D. The model was evaluated with velocity measurements, and the results were determined to be in good agreement. By inverting the 2016-2019 field monitoring results, the model shows that the preferred velocity range for Chinese sturgeon spawning is 0.6-1.5 m/s. Velocity fields of different opening modes of the generator units were simulated with identical discharge. The suitable-velocity area was maximal when all units of Dajiang Plant of Gezhouba Dam were open. For discharges below 12,000 m3/s, most of the area was suitable; for discharges above 12,000 m3/s, the suitable area rapidly decreased with increasing discharge. A comparison of suitable areas under high-flow showed that at discharges of 12,000-15,000 m3/s, opening 11-13 units on the left side was optimal. For discharges above 15,000 m3/s, all units should be open. We used these results to recommend a new operation scheme to support the conservation of Chinese sturgeon.

Gold Catalysis Enabling Furan-Fused Cyclobutenes as a Platform toward Cross Cycloadditions.

The inherently strained furan-fused cyclobutenes, in situ generated via cycloisomerizations of allenyl ketones bearing cyclopropyl moiety under gold catalysis, have been utilized as reactive building blocks toward cross cycloadditions. The [4 + 2] and [3 + 2] annulations of these species with benzo[c]isoxazoles and N-iminoquinazolinium ylides furnish various three-dimensional cyclobutane-bridged polyheterocycles in good yields. A wide range of typically electron-deficient 1,3-dienes, heterodienes, and 1,3-dipoles can trap furan-fused cyclobutenes to afford several polycyclic architectures.

Ruthenium-catalyzed coupling of α-carbonyl phosphoniums with sulfoxonium ylides via C-H activation/Wittig reaction sequences.

A Ru(ii)-catalyzed coupling of various α-carbonyl phosphoniums with sulfoxonium ylides has been realized for the facile synthesis of 1-naphthols in good to excellent yields. This oxidant-free transformation proceeds through Ru-catalyzed C-H activation of phosphoniums, Ru-carbene insertion, and intramolecular Wittig reaction processes.

Palladium-catalyzed hydroalkylation of methylenecyclopropanes with simple hydrazones.

A palladium-catalyzed hydroalkylation reaction of methylenecyclopropanes via highly selective C-C σ-bond scission was achieved under mild conditions, in which simple hydrazones served as carbanion equivalents. This method featured good functional group compatibility, affording high yields of C-alkylated terminal alkenes.

Electrolysis promoted reductive amination of electron-deficient aldehydes/ketones: a green route to the racemic clopidogrel.

An electrocatalytic reductive amination of electron-deficient aldehydes/ketones was developed, which could be used in the synthesis of functionalized tertiary amines and large scale preparation of racemic clopidogrel. A plausible mechanism involving an iminium cation intermediate was proposed.

Stereoselective and regioselective 5-exo-dig cyclization of 8-alkynylnaphthalen-1-amines for the synthesis of (E)-2-(arylthio)alkylene-1,2-dihydrobenzo[cd]indoles.

A palladium and iodine-cocatalyzed 5-exo-dig aza-thiocyclization of 8-alkynylnaphthalen-1-amines for the synthesis of (E)-2-alkylene-1,2-dihydrobenzo[cd]indole thioethers is reported. As a result of broad reaction scope, simple operation, mild conditions, and high stereoselectivity and regioselectivity, this reaction should have potential utility in organic synthesis.

Silver-Catalyzed Stereoselective Cyclization to Polysubstituted ( Z)-1,2-Dihydrobenzo[ cd]indoles.

Silver-catalyzed stereoselective synthesis of polysubstituted ( Z)-1,2-dihydrobenzo[ cd]indoles from 8-ethynylnaphthalen-1-amines is reported. In this protocol, a series of nitrogen-containing heterocyclic compounds were synthesized by silver-catalyzed α-addition of an alkyne bond with high selectivity and high yields. The synthesized polysubstituted 1,2-dihydrobenzo[ cd]indoles could be easily converted to benzo[ cd]indol-2(1 H)-ones, and both 1,2-dihydrobenzo[ cd]indoles and benzo[ cd]indol- 2(1 H)-ones are biological and pharmaceutical cores.

Synthesis of α-Methylene-ß-lactams Enabled by Base-Promoted Intramolecular 1,2-Addition of N-Propiolamide and C-C Bond Migrating Cleavage of Aziridine.

A formal α-addition of N-propiolamide and 2-bromoacetate is reported for the synthesis of α-methylene-ß-lactam in good yields. The transformation proceeds smoothly in the presence of K2CO3 as a base and KI as an additive. An excellent reaction scope is observed. A 2 mmol scaled synthesis of α-methylene-ß-lactams and synthetic applications of α-methylene-ß-lactams are also reached. In the process, it is believed that an intramolecular 1,2-addition of N-propiolamide and sequential C-C bond migrating cleavage are involved.

Synthesis of benzothiophene and indole derivatives through metal-free propargyl-allene rearrangement and allyl migration.

An efficient base-catalyzed protocol for the synthesis of benzothiophene is described. The reaction proceeds via base-promoted propargyl-allenyl rearrangement followed by cyclization and allyl migration. Phosphine-substituted indoles can be synthesized by a similar strategy.

Nucleophilic Functionalizations of Aniline Derivatives: Aromatic Pummerer Reaction for Umpolung Halogenation and Hydroxylation on Benzene Ring.

In this paper, a metal-free protocol of nucleophilic ortho-halogenation and hydroxylation of anilines via an aromatic Pummerer process is reported.