An efficient, green, and novel method for the synthesis of N-heterocycle-fused quinoxalines is reported herein. Dimethyl sulfoxide was used as both a reactant and a solvent in this reaction. A wide range of products in moderate to excellent yields were obtained, including pyrrolo[1,2-a]quinoxalines, indolo[1,2-a]quinoxalines, 1H-pyrrolo[3,2-c]quinolines, and benzo[4,5]imidazo[1,2-c]quinazolines.

AbstractA large library of 5,8-distyrylquinoxaline fluorophores was synthesized in good-to-excellent yields via a palladium-catalyzed oxidative C–H/C–H cross-coupling of electron-deficient fluorinated quinoxalines with electron-rich styrenes. The resulting quinoxaline fluorophores (Qu-Fluors) exhibited tunable color emissions with the quantum yields of up to 83% and large Stokes shifts of up to 6236 cm−1 in dichloromethane. The bioimaging performance of the Qu-Fluors was shown to have potential as near-infrared fluorescent probes for mitochondria.

A practical and concise protocol for the efficient synthesis of pyrrolo[1,2-a]quinoxalines from readily available α-amino acids and 2-(1H-pyrrol-1-yl)anilines under transition metal-free conditions has been established. This protocol, which includes the formation of new C–C and C–N bonds, features a wide substrate scope with a broad range of functional group tolerance.

A one-pot protocol for the synthesis of structurally diverse 2-hetarylbenzothiazoles via oxidative condensation of the sp3 C–H bond with benzothiazoles has been described. This process is metal free and operationally simple. A series of 2-hetarylbenzothiazoles were prepared in moderate to good yield under mild conditions.

An efficient protocol for the synthesis of trisubstitued pyrrolo[1,2-a]pyrazines through three components cyclization and one-pot cascade reaction is presented. Various trisubstitued pyrrolo[1,2-a]pyrazines are obtained by this metal-free process in moderate to good yields.Download high-res image (97KB)Download full-size image

A simple, one-pot and copper-catalyzed coupling reaction for the construction of 1,2-disubstituted benzimidazole derivatives is described. A low-cost copper salt and a weak base K3PO4 were utilized in this reaction. A variety of 1,2-disubstituted benzimidazoles were obtained in moderate to excellent yields.

A copper-catalysed three-component reaction for constructing a series of quinazoline derivatives has been developed. In this system, solvents act as the reactants and different functional groups are well tolerated to obtain corresponding products in moderate to good yields.

A copper-catalyzed process for the synthesis of pyrrolo[1,2-a]quinoxalines from readily available α-amino acids and 1-(2-halophenyl)-1H-pyrroles is described. Different functional groups were well tolerated to give the corresponding products.

A facile and efficient method was developed for the synthesis of isothiazolo[5,4-b]pyridin-3(2H)-one derivatives. This new type of AIE materials was studied through photophysical analysis, X-ray and theoretical calculations. Then, based on a ring-opening reaction, we found a useful application of this material in cysteine and glutathione detection.

An unprecedented palladium-catalyzed oxidative annulation of acrylamides with benzyne precursors has been successfully developed. By using this mild “N–H activation/Heck reaction” method, a wide variety of quinolinones were conveniently prepared in one step with high efficiency.

An efficient iodine–DMSO catalyzed system for the synthesis of quinoxaline derivatives was developed. The construction of this quinoxaline system went through a one-pot oxidation/cyclization process. The reaction afforded a variety of products in good to excellent yields. This methodology has potential applications in the synthesis of biologically and medicinally relevant compounds.

A new method for the synthesis of furan-substituted allenes via Cu(I)-catalyzed coupling of conjugated ene-yne-ketones with terminal alkynes has been developed. A wide range of functional groups are tolerated, and the products are obtained in good to excellent yields under mild conditions. A copper carbene migratory insertion is proposed as the key step in this transformation with conjugated ene-yne-ketones as carbene precursors.

A one-pot transition metal-free methodology for constructing pharmacologically active dibenzodiazepine derivatives was developed. Fluoro-, bromo- and nitro-substituted aryl aldehydes were applied to this reaction efficiently.

A one-pot transition metal-free method for synthesizing benzo[4,5]imidazo[1,2-a]quinazoline and imidazo[1,2-a]quinazoline derivatives has been developed. The approach is widely applicable to 2-fluoro-, 2-chloro-, 2-bromo- and 2-nitro-substituted aryl aldehyde and ketone substrates. The fluorescence properties of target compounds were studied.Keywords: benzo[4,5]imidazo[1,2-a]quinazoline derivatives; fluorescence property; one-pot synthesis; transition metal-free

A series of 1,4-thiazepin-5(4H)-one derivatives were synthesized via a transition metal-free one-pot Smiles rearrangement process at room temperature. Regioselective seven-membered heterocycles were constructed in good to excellent yields. To gain an in-depth understanding of the S–N type Smiles rearrangement mechanism, a theoretical study was also performed by quantum chemistry calculations.

A copper-catalyzed one-pot process for the construction of benzo[4,5]imidazo[1,2-a]quinoxalines under air is described. Aryl chlorides, aryl bromides, and aryl iodides can be applied to the synthesis of these compounds.

A transition metal-free methodology for the synthesis of pyridazinopyrido[3,2-f][1,4]thiazepine-diones was studied. The construction of this tricyclic system went through a one-pot coupling/Smiles rearrangement/cyclization process. The high yields of pure products were obtained through simple recrystallization.

A convenient and efficient copper-catalyzed one-pot process for the construction of 6H-benzo[b]benzo[4,5]imidazo[1,2-d][1,4]oxazines through reactions of 2-halophenols with 2-(chloromethyl)-1H-benzo[d]imidazoles under mild conditions is described. The reactions afforded a variety of products in good to excellent yields.

A one-pot synthetic protocol involving 1,3-dipolar cycloaddition/deprotonation/elimination/oxidation for the construction of indolizines has been proposed from easily available pyridine derivatives and γ-bromo-crotonates via a metal-free tandem process. A variety of indolizine derivatives were synthesized under mild conditions. Noteworthy features of this synthetic strategy are short reaction time, using air as oxidant and mild reaction conditions.

A wide range of substituted α-arylated ketones were synthesized in moderate to excellent yields via a Truce Smiles rearrangement. The main scaffold has various applications in medical and biochemical fields. This process also provides a facile and direct method for the C–C bond formation.

A series of transition metal-free tandem reactions for the synthesis of indolizines and 6,7-dihydroindolizin-8(5H)-ones by 4-bromobut-2-enoate ramifications reacted with 2-acetyl pyrrole derivatives are described. As the α-carbon changed from CH3, CH2Cl, CHCl2, to CCl3, different kinds of tandem reactions were observed. These tandem reactions could be used to synthesize fused indolizine and indolizidine scaffolds under mild and green conditions.

An efficient one-pot tandem method for the synthesis of pyridazino[4,5-b][1,4]thiazine-diones via Smiles rearrangement was developed. A number of ideal products were obtained with high yields without any byproducts. More specifically, this transition metal-free process is an environmentally friendly, economical, and efficient method for preparation of mixture-based heterocyclic libraries.

Benzo[d]imidazo[2,1-b]thiazole analogues were synthesized via a one-pot metal-free procedure. A series of benzene and pyridine substrates were employed to the methodology. The desired products were generated in moderate to good yields. The effect of substituent group had also been studied.

A facile and efficient approach to 1,4-benzooxazinone or 1,4-pyridooxazinone scaffolds is developed via Smiles rearrangement tandem reaction. 1,4-Benzooxazinones or 1,4-pyridooxazinones with diversity at two substituents on their scaffolds were synthesized conveniently in the presence of cesium carbonate at room temperature in good to excellent yields. The reaction mechanism is assumed by a tandem coupling/Smiles rearrangement/cyclization process.

Benzo[1,4]thiazin-3(4H)-one derivatives are conveniently prepared in one pot via a Smiles rearrangement (SR) tandem reaction. In order to understand the reaction, we present here a theoretical study on the S–N type SR mechanism.

A transition metal-free process for the regioselective synthesis of pyrrolo[1,2-a]quinoxalines under mild conditions in one-pot is described. The reaction afforded a variety of products in good to excellent yields. Indolo[1,2-a]quinoxalines were also synthesized from indole-2-carboxamides under the same conditions.

The paper describes a convenient and facile methodology for the regioselective synthesis of fused oxazepinone scaffolds. This process is an efficient construction of the oxazepinone scaffold by a one-pot coupling/Smiles rearrangement/cyclization approach. This transition metal-free process has potential applications in the synthesis of biologically and medicinally relevant compounds.Keywords: coupling/Smiles rearrangement/cyclization process; fused oxazepinone scaffolds; one-pot

Indolocarbazole derivatives have already been reported to be good organic semiconductor candidates. The knowledge of the relationship between the structure and packing of molecules in crystal is indispensable in design of high performance organic semiconductor materials. Two new indolocarbazole derivatives, 2,8-dibromo-5,11-di-[4-(isoindole-1,3-dione-2-yl)butyl]indolo[3,2-b]carbazole (I) and 2,8,6,12-tetrabromo-5,11-di-(4-chlorobutyl)indolo[3,2-b]carbazole (II) have been synthesized and the crystal structures have been studied. The dichloromethane solvate of (I), C42H32Br2N4O4 · 2CH2Cl2, is monoclinic, space groups P21/n. Unit cell parameters are a = 11.6847(2), b = 12.6942(2), c = 13.7899(2) Å, β = 91.8220(10)°. Unlike other indolo[3,2-b]carbazole derivatives, there is no any π–π stacking between the indolocarbazole backbone of two adjacent molecules in the crystal. Since the isoindole-1,3-dione-2-yl is introduced in 5- and 11-positions in the molecule, the intermolecular short contacts mainly localize in between the pendant groups of the neighboring indolocarbazole molecules. The compound (II) is also monoclinic with P21/c space groups. Unit cell parameters are a = 4.6427(9), b = 11.425(2), c = 24.511(4) Å, β = 93.47(1)°. In contrast with compound (I), the molecules of (II) possess strong face-to-face π–π stacking. The crystal structures were studied in detail. It is concluded that linear pedant groups benefit to co-facial π–π interaction. Additionally, the molecule electronic spectra were studied by quantum chemistry theoretical calculation.

A new method for the synthesis of 2-hetarylquinazolin-4(3H)-ones from 2-aminobenzamides and (2-azaaryl)methanes under transition metal-free conditions is described. This protocol features a wide substrate scope with a broad range of functional group tolerance under mild conditions. The oxidation of (2-azaaryl)methanes to (2-azaaryl)methanals is proposed as the key step in this transformation.

A one-pot protocol for the synthesis of structurally diverse 2-hetarylbenzothiazoles via oxidative condensation of the sp3 C–H bond with benzothiazoles has been described. This process is metal free and operationally simple. A series of 2-hetarylbenzothiazoles were prepared in moderate to good yield under mild conditions.

A simple, one-pot and copper-catalyzed coupling reaction for the construction of 1,2-disubstituted benzimidazole derivatives is described. A low-cost copper salt and a weak base K3PO4 were utilized in this reaction. A variety of 1,2-disubstituted benzimidazoles were obtained in moderate to excellent yields.

An efficient and convenient one-pot domino reaction for the direct synthesis of pyrrolo[1,2-a]quinoxalines has been developed. This approach utilizes an imine formation reaction, SEAr reaction and cleavage of C–C bonds catalyzed by a Brønsted acid. β-Diketones and β-keto esters are both well tolerated to give the corresponding products in moderate to excellent yields.

A one-pot transition-metal-free approach for the synthesis of indole-fused dibenzo[b,f][1,4]oxazepines from 2-(1H-indol-2-yl)phenol and 1,2-dihalobenzenes or 2 halonitroarenes has been developed. The proposed mechanism for this transformation features a Smiles rearrangement favoured over a direct intramolecular nucleophilic cyclization, which affords the corresponding products in different regioselectivities. This reaction also features simple reaction conditions and wide functional group tolerance.

An efficient I2-catalyzed cascade coupling protocol was developed for the synthesis of pyrrolo[1,2-a]quinoxaline and imidazo[1,5-a]quinoxaline derivatives via sp3 and sp2 C–H cross-dehydrogenative coupling. A nontoxic, readily available catalyst, I2, and an oxidant, DMSO, were used in this metal-free process. The target compounds were obtained in good-to-excellent yields with a broad substrate scope.

A copper-catalysed three-component reaction for constructing a series of quinazoline derivatives has been developed. In this system, solvents act as the reactants and different functional groups are well tolerated to obtain corresponding products in moderate to good yields.

A one-pot transition metal-free methodology for constructing pharmacologically active dibenzodiazepine derivatives was developed. Fluoro-, bromo- and nitro-substituted aryl aldehydes were applied to this reaction efficiently.

Benzo[d]imidazo[2,1-b]thiazole analogues were synthesized via a one-pot metal-free procedure. A series of benzene and pyridine substrates were employed to the methodology. The desired products were generated in moderate to good yields. The effect of substituent group had also been studied.

A transition metal-free methodology for the synthesis of pyridazinopyrido[3,2-f][1,4]thiazepine-diones was studied. The construction of this tricyclic system went through a one-pot coupling/Smiles rearrangement/cyclization process. The high yields of pure products were obtained through simple recrystallization.

A transition metal-free process for the regioselective synthesis of pyrrolo[1,2-a]quinoxalines under mild conditions in one-pot is described. The reaction afforded a variety of products in good to excellent yields. Indolo[1,2-a]quinoxalines were also synthesized from indole-2-carboxamides under the same conditions.