Rhodium(III)-Catalyzed Sequential Cyclization of Enaminones with 1,3-Dienes via C-H Activation for the Synthesis of Fluorenones.

An efficient method for construction of various fluorenones has been achieved via Rh(III)-catalyzed C-H activation/[4 + 2] annulation/aromatization sequences of simple and readily available enaminones and 1,3-dienes. This protocol showed good substrate compatibility as an array of structurally and electronically diverse fluorenones prepared efficiently in moderate to good yields and preparative scale utility showing very good efficiency in the late-stage functionalization of complex valuable molecules.

Molecular-Oxygen-Mediated Multicomponent Oxidative Cyclization: Synthesis of Tertiary-Alcohol-Unit-Bearing -Heterocycles via Transforming C-H to C-OH Bonds.

We developed a molecular-oxygen-mediated multicomponent oxidative cyclization strategy to synthesize -heterocycles containing tertiary alcohol units via the formation of key C-OH bonds and quaternary carbon centers. This formal [3 + 2 + 1] annulation offers a green and sustainable alternative for the C-OH bond formation, using O as both the oxidant and oxygen source under metal- and catalyst-free conditions. Notably, continuous [1,5]-hydrogen transfer together with excess alcohols promotes the formation of C-OH-bearing products.

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

The unprecedented dimerizations of 2-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.

Cu(II)-catalyzed domino construction of spironaphthalenones by dearomatization of β-naphthols and using ,-dimethylaminoethanol as a C1 synthon.

Herein, a Cu(II)-catalyzed facile construction of synthetically valuable spiro compounds from β-naphthols in air is reported, in which ,-dimethylaminoethanol (DMEA) serves as an efficient and unique C1 synthon. This transformation proceeds through an -quinone methide (-QM) formation/Michael addition/dearomatization sequence, affording various spiro(naphthalenenaphtho)furan-2-ones in moderate to excellent yields.

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

The metal-free cyclization of allenyl ketones and -toluenesulfonylmethyl isocyanide (TosMIC), promoted by CsCO, 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.

Application of ,-Dimethylethanolamine as a One-Carbon Synthon for the Synthesis of Pyrrolo[1,2-]quinoxalines, Quinazolin-4-ones, and Benzo[4,5]imidazoquinazolines [5 + 1] Annulation.

The synthesis of -heterocycles composes a significant part of synthetic chemistry. In this report, a Cu(II)-catalyzed green and efficient synthesis of pyrrolo[1,2-]quinoxaline, quinazolin-4-one, and benzo[4,5]imidazoquinazoline derivatives was developed, employing -dimethylethanolamine (DMEA) as a C1 synthon. Green oxidant O is critical in these transformations, facilitating the formation of a key intermediate─a reactive iminium ion.

Facile construction of ,-disulfonated 5-amino pyrazoles through an iodine-catalyzed cascade reaction.

A green and facile synthesis of previously unreported ,-disulfonated 5-amino pyrazoles was established through an iodine-catalyzed cascade reaction of easily accessible sulfonyl hydrazides, β-ketonitriles, and sodium sulfinates. Diverse ,-disulfonated 5-amino pyrazoles could be obtained in 38-88% yields. This methodology features green and mild conditions, broad substrate scope, and effortless work-up.

Rhodium(III)-Catalyzed Sequential Cyclization of -Boc Hydrazones with Propargylic Monofluoroalkynes via C-H Activation/C-F Cleavage for the Synthesis of Spiro[cyclobutane-1,9'-indeno[1,2-]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 -Boc hydrazones and propargylic monofluoroalkynes afforded fused tetracyclic spiro[cyclobutane-1,9'-indeno[1,2-]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 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.

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

The inherently strained furan-fused cyclobutenes, 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[]isoxazoles and -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.

Identification and Speciation of Nanoscale Silver in Complex Solid Matrices by Sequential Extraction Coupled with Inductively Coupled Plasma Optical Emission Spectrometry.

Nanoscale silver (n-Ag) including silver nanoparticles (Ag-NPs), silver chloride nanoparticles (AgCl-NPs), and silver sulfide nanoparticles (AgS-NPs) and their corresponding ionic counterpart, namely, dissolved Ag, may coexist in soils. X-ray absorption near edge spectroscopy (XANES) is used to elucidate the speciation of n-Ag in soils, whereas it possesses drawbacks like high costs, rare availability of the instrument, and providing semiquantitative data. We developed a new method for the identification and speciation of n-Ag in soils and sediments based on a sequential extraction technique coupled with inductively coupled plasma optical emission spectrometry.

Gold(I)-Catalyzed [8+4] Cycloaddition of 1,4-All-Carbon Dipoles with Tropone.

Herein, we describe a gold(I)-catalyzed generation of nonclassical gold-containing 1,4-all-carbon dipoles from cycloisomerization/1,2-carbene transfer/ring opening cascade reactions of readily accessible allenyl ketones bearing a cyclopropyl moiety and its cyclization with tropone. This method features an unprecedented formal [8+4] high-order cycloaddition under mild conditions for delivering structurally complex 7,7,5-tricycles in generally moderate to high yields.

Tunable Gold(I)-Catalyzed [4 + 3] Cycloaddition for Divergent Synthesis of Furan-Fused N,O-Heterocycles.

By choosing suitable ligand-directed gold catalysts, two types of gold-containing all-carbon 1,4-dipoles could be generated selectively from the gold(I)-catalyzed cycloisomerizations of allenyl ketones bearing a cyclopropyl moiety, which undergo [4 + 3] cycloadditions with nitrones to produce two regiomers of furan-condensed N,O-seven-membered rings in moderate to excellent yields highly selectively.

Iron(III)-Mediated Bicyclization of 1,2-Allenyl Aryl Ketones: Assembly of Indanone-Fused Polycyclic Scaffolds and Dibenzo[,]pentalene Derivatives.

The rapid construction of three-dimensional fused carbocycles is a key challenge in synthetic chemistry. Herein, an unprecedented and practical tandem Nazarov/oxidative umpolung 4π-ring closure of readily available 1,2-allenyl aryl ketones mediated by iron(III) chloride has been developed, furnishing a new family of indanone-fused molecular architectures in moderate to excellent yields. The indanone-containing blocks can be efficiently converted to unsymmetrical dibenzo[,]pentalenes.

Synthesis of 5 H-Dibenzo[ c, g]chromen-5-ones via FeCl-Mediated Tandem C-O Bond Cleavage/6π Electrocyclization/Oxidative Aromatization.

A novel and expedient method for transformation of readily available 1-isochromanones bearing a diaryl allenic moiety at the C4-position to functionalized 5 H-dibenzo[ c, g]chromen-5-ones under mild conditions is developed. This strategy is based on the dual abilities of iron(III) chloride to promote selective C-O bond cleavage/6π electrocyclization and an oxidative aromatization sequence.

Transition-Metal-Free Arylation and Alkylation of Diarylmethyl p-Tolyl Sulfones with Zinc Reagents.

The transition-metal-free synthesis of unsymmetrical and highly functionalized triarylmethanes through arylation of the situ generated o-QMs from diarylmethyl p-tolyl sulfones with aryl zinc reagents is described. Alkyl zinc reagents are also well tolerated in this reaction. Additionally, the straightforward synthesis of the analogue of the antituberculosis agent A and the key precursor of the anti-breast-cancer agent B are achieved by this strategy.

1,2-Gold Carbene Transfer Empowers Regioselective Synthesis of Polysubstituted Furans.

A gold-catalyzed cascade cycloisomerization/ring-opening reaction of allenyl ketones bearing a cyclopropyl moiety with a wide variety of alcohols or ketones is developed. This reaction involves an unprecedented 1,2-gold carbene transfer to provide regioselective and modular access to tri- or tetrasubstituted furans in moderate to high yields and with broad substrate tolerability.

Oxidative Asymmetric [2 + 3] Annulation of Aldehydes with Azomethine Imines Enabled by N-Heterocyclic Carbene Catalysis.

An efficient asymmetric [2 + 3] annulation of simple aldehydes with N,N'-cyclic azomethine imines via oxidative N-heterocyclic carbene (NHC) catalysis is disclosed, affording bicyclic pyrazolidinones bearing two vicinal tertiary stereogenic centers with moderate to good yields (56-84% for 19 examples), good to excellent diastereoselectivities (>20:1 for 17 examples), and good to excellent enantioselectivities (66-98% for 19 examples). This direct α-carbon functionalization reaction of aldehyde can be readily performed on gram scale under mild conditions, and a five-membered transition state is proposed to rationalize the stereochemical outcome.

Strain-Promoted Nitration of 3-Cyclopropylideneprop-2-en-1-ones and the Application for the Synthesis of Pyrroles.

The tunable nucleophilic nitration of 3-cyclopropylideneprop-2-en-1-ones with cheap sodium nitrite is described. This transformation proceeds with the assistance of a strained cyclopropane ring and allows for a divergent route to various synthetically useful β,γ-dinitro or γ-mononitro adducts in high yields with exclusive regio- and stereoselectivity. Additionally, a wide array of valuable functionalized N-unprotected pyrroles is achieved from the resulting β,γ-dinitro compounds via reductive cyclization strategy.

Base-mediated diastereoselective [4 + 3] annulation of in situ generated ortho-quinone methides with C,N-cyclic azomethine imines.

An efficient [4 + 3] annulation of 2-(1-tosylalkyl)phenols with C,N-cyclic azomethine imines via in situ generation of ortho-quinone methides (o-QMs) under mild basic reaction conditions is disclosed, furnishing biologically interesting seven-membered heterocyclic compounds with moderate to good yields and excellent diastereoselectivities. A gram-scale reaction is performed to demonstrate the potential in industrial application and two transition states are proposed to rationalize the outstanding diastereoselectivity.

Enantioselective [2+2] annulation of simple aldehydes with isatin-derived ketimines via oxidative N-heterocyclic carbene catalysis.

An asymmetric [2+2] annulation reaction through direct α-carbon functionalization of simple aldehydes via oxidative N-heterocyclic carbene catalysis is disclosed. These in situ generated triazolium enolate intermediates undergo a highly stereoselective Mannich reaction with isatin-derived ketimines followed by intramolecular lactamization to afford enantioenriched spirooxindole β-lactams bearing two vicinal stereogenic centers.

Catalyst-Controlled Chemodivergent Modification of Indoles with 2-Furylcarbinols: Piancatelli Reaction vs Cross-Dehydrative Coupling Reaction.

A divergent synthetic strategy to functionalize the indole nucleus with readily available 2-furylcarbinols was developed. It was found that the 3-(4-oxo-2-cyclopentenyl)indoles were obtained in moderate to good yields (up to 89%) through Piancatelli reaction catalyzed by ZnCl, whereas employment of Brønsted acid TFA afforded directly coupled product 3-(2-furyl)indoles in moderate to good yields (up to 87%) via the deprotonation-rearomatization route.

1-Hydroxybenzotriazole-Assisted, N-Heterocyclic Carbene Catalyzed β-Functionalization of Saturated Carboxylic Esters: Access to Spirooxindole Lactones.

A 1-hydroxybenzotriazole-assisted, N-heterocyclic carbene catalyzed direct β-functionalization of saturated carboxylic esters is disclosed. This formal [3 + 2] annulation reaction of carboxylic esters with isatins affords optically pure spirooxindole lactones (on gram scale) bearing two vicinal stereogenic centers. A dual role of HOBt is proposed based on controlled experiments to rationalize the enhancement of diastereoselectivity and enantioselectivity.

Solvent-Controlled, Tunable Hydrosulfonylation of 3-Cyclopropylideneprop-2-en-1-ones.

An interesting and tunable hydrosulfonylation of 3-cyclopropylideneprop-2-en-1-ones with sodium sulfinates and acetic acid is described. The corresponding β- or γ-addition products can be produced in good to excellent yields with high selectivities, respectively. A rationale for these transformations is proposed base on the controlled experiments.