Rh(III)-Catalyzed Reaction of 4-Diazoisochroman-3-imines with (2-Formylaryl)boronic Acids To Access a Straightforward Construction of 5H-Isochromeno[3,4-c]isoquinolines.

An Rh(III)-catalyzed one-pot synthesis of 5H-isochromeno[3,4-c]isoquinolines from readily available 4-diazoisochroman-3-imines and (2-formylphenyl)boronic acids is reported. The cascade annulation involves a Rh(III)-catalyzed cross-coupling and an intramolecular nucleophilic addition-elimination process. A series of biologically important 5H-isochromeno[3,4-c]isoquinolines were obtained in good to excellent yields. The method can be extended to synthesize 7H-isochromeno[3,4-b]thieno[3,2-d]pyridines and 7H-isochromeno[3,4-b]thieno[2,3-d]pyridines from the corresponding heteroaryl boronic acids.

Olefination of 3-Diazoindolin-2-imines with Hydrazones: An Approach toward Stereoselective Synthesis of (E)-3-Arylideneindolin-2-imines.

Stereoselective synthesis of (E)-3-arylideneindolin-2-imines from 3-diazoindolin-2-imines and hydrazones was achieved using copper bromide as the catalyst. The olefination reaction proceeded via copper-catalyzed aerobic oxidation of hydrazones to diazo compounds and copper-catalyzed cross coupling of two different diazo components in a tandem manner.

Cu(II)-Catalyzed Synthesis of 4-(1,4,5,6-Tetrahydropyridin-3-yl)-1,4-dihydroisoquinolin-3-ones from 4-Diazoisoquinolin-3-ones.

We report a simple, efficient, and highly selective C-H bond insertion of copper carbenes generated in situ from 4-diazo-1,4-dihydroisoquinolin-3-ones into ß-C(sp2)-H bonds of N-sulfonyl enamides, which gave a series of 4-(1,4,5,6-tetrahydropyridin-3-yl)-1,4-dihydroisoquinolin-3(2H)-ones in good to excellent yields. Operationally simple and mild reaction conditions, a cheap catalyst, readily accessible starting materials, and a broad substrate scope are the merits of this reaction.

Synthesis of Functionalized Indolobenzazepinones via Sc(OTf)3-Induced Ring Expansion/Annulation Reactions of 4-Diazoisoquinolin-3-ones with Isatins.

Herein, we report an unexpected cascade ring expansion/annulation reaction between 4-diazo-1,4-dihydroisoquinolin-3-ones and a variety of isatin derivatives in the presence of Sc(OTf)3 catalyst. A series of novel indolobenzazepinones were synthesized in good to excellent yields with the exclusion of nitrogen and carbon dioxide gases. High bond-forming efficiency, novel reaction mechanism, readily available starting materials, commercially available cheap catalyst, broad substrate scope, and mild reaction conditions are the prominent features of this method.

Rh(II)-catalyzed synthesis of 5H-isochromeno[3,4-b]indolizines from 4-diazoisochroman-3-imines and pyridines.

A Rh(II)-catalyzed (3 + 2) annulation of pyridines with 4-diazoisochroman-3-imines leading to 5H-isochromeno[3,4-b]indolizines is presented. This methodology provides straightforward access to a wide variety of substituted 5H-isochromeno[3,4-b]indolizines with moderate to good yields (up to 84%) and complete regioselectivity.

Rh(III)-Catalyzed C-H bond activation/annulation reactions of arylacyl ammonium salts with 4-diazoisochroman-3-imines and 4-diazoisoquinolin-3-ones.

Herein, we report a C-H bond functionalization strategy for the construction of oxo- and aza-spirocyclic compounds from diazo compounds as coupling partners. Our method comprises ortho sp2 C-H bond activation of arylacyl ammonium salts, followed by coupling with two types of cyclic diazo compounds i.e. 4-diazoisochroman-3-imines and 4-diazoisoquinolin-3-ones, respectively. The mechanism involves the formation of dual metal carbene intermediates in situ with the breakage of oxidizing C-N bonds in arylacyl ammonium salts. The cascade C-H activation/annulation process gave a variety of novel spiro[indene-1,4'-isochromane]-3,3'(2H)-diones and spiro[indene-1,4'-isoquinoline]-3,3'(2H)-diones in good to excellent yields. Readily available starting materials, broad substrate scope, and operationally simple and mild reaction conditions are the prominent features of this method.

Base Promoted Three-Component Annulation of 4-Diazoisochroman-3-imines with Dimethylsulfonium Ylides: Synthesis of Highly Functionalized Isochromeno[4,3-c]pyridazines.

A novel method has been developed to synthesize a unique class of highly functionalized isochromeno[4,3-c]pyridazines. This reaction features an intermolecular functionalization of terminal nitrogen atom of diazo group of 4-diazoisochoman-3-imine with two dimethylsulfonium ylide components, followed by a base promoted 6-exo-trig cyclization step. Readily available starting materials, a broad substrate scope, and operationally simple, mild, and catalyst-free reaction conditions are the prominent features of this method.

Photocatalytic Approach for Construction of 5,6-Dihydroimidazo[2,1-a]isoquinolines and Their Luminescent Properties.

A visible-light-driven photoredox reaction of tetrahydroisoquinoline with 2H-azirines is described. 4,7-Bis(4-methoxyphenyl)benzo[c][1,2,5]thiadiazole, a benzothiadiazole (BTD) derived fluorophore, is used as an organic photoredox catalyst, and the reaction offers an efficient access to 5,6-dihydroimidazo[2,1-a]isoquinolines with a broad range of functional groups. The resulting 5,6-dihydroimidazo[2,1-a]isoquinolines present strong photoluminecence in solutions and powders and could be applied in the fabrication of blue OLED devices.

Visible-Light-Induced Photocatalyst-Free Aerobic Hydroxyazidations of Indoles: A Highly Regioselective and Stereoselective Synthesis of trans-2-Azidoindolin-3-ols.

A visible-light-promoted aerobic hydroxyazidation of indole derivatives with TMSN3 is described. The reaction proceeded under photocatalyst-free conditions to furnish trans-2-azidoindolin-3-ols with high regioselectivity and stereoselectivity. The protocol is operationally simple, and the starting materials (e.g., 1-(pyrimidin-2-yl) indoles, azidotrimethylsilane, and air) are readily available. The proposed mechanism in which substrates act as photocatalysts upon excitation using blue light-emitting diodes (LEDs) was supported by experimental studies.

Visible-Light-Induced C(sp2)-C(sp3) Coupling Reaction for the Regioselective Synthesis of 3-Functionalized Coumarins.

A photocatalysis strategy for the regioselective synthesis of 3-functionalized coumarins is reported. With visible light irradiation, a direct and regioselective C(sp2)-C(sp3) coupling reaction of 3-(2-hydroxyphenyl)acrylates with ethers or thioethers occurs by using Ru(bpy)3Cl2·6H2O as a photocatalyst and TBHP as an oxidant. The cascade process involves alkenylation of the C(sp3)-H bond of ethers and lactonization, furnishing 3-alkylated coumarins as the final products. This approach is characterized by a broad substrate scope, mild reaction conditions, and simplified operation. The synthesis of 3-alkylated coumarins could be realized by a one-pot procedure, starting from commercially available salicylaldehyde.

Syntheses of 4-allyl-/4-allenyl-4-(arylthio)-1,4-dihydroisoquinolin-3-ones via the photochemical Doyle-Kirmse reaction.

Facile synthesis of 4-allyl-/4-allenyl-4-(arylthio)-1,4-dihydroisoquinolin-3-ones via the visible-light-induced Doyle-Kirmse reaction of 4-diazo-1,4-dihydroisoquinolin-3-ones with allyl-/propargyl sulfides is reported. The reaction proceeds via the generation of free carbenes from cyclic diazo compounds followed by in situ formation of sulfonium ylide intermediates, which subsequently undergo [2,3-sigmatropic rearrangement] to give highly functionalized dihydroisoquinolinones in moderate to good yields. Broad substrate scope, and catalyst-free and mild conditions are the merits of this reaction.

Syntheses of 2-Iminoindolin-3-ones and 2-Alknyl-2,3-dihydroquinazolin-4(1H)-ones from 3-Diazoindolin-2-imines.

3-Diazoindolin-2-imines reacted with nitrones to furnish 2-iminoindolin-3-ones through a Au(I)-catalyzed cascade oxygen transfer/imine exchange process. The prepared 2-iminoindolin-3-ones could be further transformed into 2-alknyl-2,3-dihydroquinazolin-4(1H)-ones through a Ag(I)-catalyzed reaction with terminal alkynes. A MeOH-triggered ring expansion mechanism involving cyclic iminium formation and nucleophilic addition is proposed for this novel alkynylation reaction. This two-step procedure provides a general and convenient approach to 2-alknyl-2,3-dihydroquinazolin-4(1H)-ones, which are privileged structures in medicinal chemistry.

Synthesis of 8-Alkoxy-5H-isochromeno[3,4-c]isoquinolines and 1-Alkoxy-4-arylisoquinolin-3-ols through Rh(III)-Catalyzed C-H Functionalization of Benzimidates with 4-Diazoisochroman-3-imines and 4-Diazoisoquinolin-3-ones.

Rh(III)-catalyzed C-H activation/annulation of benzimidates with 4-diazoisochroman-3-imines furnished 8-alkoxy-5H-isochromeno[3,4-c]isoquinolines in moderate to excellent yields with a broad range of substrate scope. The reaction was carried out under mild reaction conditions and could be scaled up with practical usage. Similar reaction between benzimidates and 4-diazoisoquinolin-3-ones provided 1-alkoxy-4-arylisoquinolin-3-ols in excellent yields. Moreover, the synthesized products could be conveniently transformed to the corresponding heterocycles with a 1,8-naphthyridinone or isochromenopyridinone core, which are privileged structures in medicinal chemistry.

TfOH-promoted synthesis of 4,5-dihydrooxazolo[5,4-c]isoquinolines via formal [3 + 2] cycloaddition of 4-diazoisoquinolin-3-one and benzonitriles.

A facile and efficient method for the synthesis of novel 2-substituted 4-tosyl-4,5-dihydrooxazolo[5,4-c]isoquinolines from 4-diazoisoquinolin-3-ones and nitriles is reported. The reaction proceeded through a TfOH-promoted formal [3 + 2] cycloaddition and the products could be conveniently converted to 2-aryloxazolo[5,4-c]isoquinolines and the subsequent 2-(oxazolo[5,4-c]isoquinolin-2-yl)phenol which emitted bright green light in dilute dichloromethane solution and in solid form as well. Simple operation, metal-free and mild reaction conditions, short reaction time and broad substrate scope are the prominent features of this methodology.

General Approach To Construct Azepino[2,3-b:4,5-b']diindoles, Azocino[2,3-b:4,5-b']diindoles, and Azonino[2,3-b:4,5-b']diindoles via Rh(II)-Catalyzed Reactions of 3-Diazoindolin-2-imines with 3-(Bromoalkyl)indoles.

Rh(II)-catalyzed reactions of 3-diazoindolin-2-imines with 3-(2-bromoethyl)indoles, 3-(3-bromopropyl)indoles, and 3-(4-bromobutyl)indoles, followed by treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in a one-pot operation furnished azepino[2,3-b:4,5-b']diindoles, azocino[2,3-b:4,5-b']diindoles, and azonino[2,3-b:4,5-b']diindoles, respectively. Structural uniqueness of the products, broad substrate scope, mild reaction conditions, and readily available starting materials are the merits of this approach.

Palladium-Catalyzed Synthesis of 3-Haloindol-2-amines from 3-Diazoindolin-2-imines and Alkyl Halides.

Synthetically valuable 3-haloindol-2-amines were prepared from readily available 3-diazoindolin-2-imines and a variety of alkyl halides through the palladium-catalyzed reaction. The broad substrate scope of both diazo compounds and alkyl halides, mild reaction conditions, and high efficiency are the main characters of this method. The synthesized 3-haloindol-2-amines can be conveniently transformed to more complex indole derivatives.

Copper-Carbene-Triggered Electrophilic Cyclization of o-Hydroxyarylenaminones with 3-Diazoindolin-2-imines: Synthesis of 3-Indolyl-4 H-chromen-4-ones and Pyrido[2,3- b:6,5- b']diindoles.

The Cu(II)-catalyzed electrophilic cyclization reaction between o-hydroxyarylenaminones and 3-diazoindolin-2-imines furnished 3-indolyl-4 H-chromen-4-ones in moderate to good yields with a broad substrate scope. Several pyrido[2,3- b:6,5- b']diindoles and one pyrazino[2,3- b:5,6- b']diindole were also obtained as byproducts in some cases and tested for their photophysical properties. Pyrido[2,3- b:6,5- b']diindoles exhibited solvent-dependent emission, while pyrazino[2,3- b:5,6- b']diindole emitted strong luminescence with 25.6% quantum yield in cyclohexane.

Preparation of spiro[imidazolidine-4,3'-indolin]-2'-imines via copper(i)-catalyzed formal [2 + 2 + 1] cycloaddition of 3-diazoindolin-2-imines and triazines.

We report a facile and efficient synthesis of spiro[imidazolidine-4,3'-indolin]-2'-imines via a copper(i)-catalyzed cascade reaction of 3-diazoindolin-2-imines with 1,3,5-triazines. The reaction proceeds under very mild conditions and tolerates a variety of functional groups. The cascade process involves the formation of a copper-carbene intermediate and a formal [2 + 2 + 1] cycloaddition.

Copper-Catalyzed Syntheses of 3-Allyl-3-arylthioindolin-2-imines and 3-Allenyl-3-arylthioindolin-2-imines from 3-Diazoindolin-2-imines.

3-Allyl-3-arylthioindolin-2-imines and 3-allenyl-3-arylthioindolin- 2-imines were synthesized via the copper-catalyzed reaction of 3-diazoindolin-2-imines with allyl and propargyl aryl sulfides, respectively. The formation of a sulfonium ylide through the reaction of allyl or propargyl aryl sulfides with copper carbene species generated from 3-diazoindolin-2-imines and subsequent [2,3]-sigmatropic rearrangement should be involved in the cascade process. The procedure is general and highly efficient for the construction of these 3,3-disubstituted indoline derivatives.

Convenient synthesis of 2-amino-3-(arylthio)indoles via the Rh-catalyzed reaction of 3-diazoindol-2-imines with thioesters.

2-Amino-3-(arylthio)indoles were conveniently synthesized via the Rh(ii)-catalyzed C-S/N-C coupling reaction between 3-diazoindol-2-imines and thioesters. The products could be further oxidized to 2-amino-3-(arylsulfonyl)indoles by m-chloroperbenzoic acid and the N-sulfonyl group could be easily removed by reduction with SmI2.