An efficient cascade reaction via trapping in situ generated active intermediate 1,4-oxazepine, formed from base-promoted 7-exo-dig cyclization reaction of N-propargyl enaminone, has been developed. Alcohols/thiols and aldehydes were used as trapping agents, providing 2-alkoxy/2-sulfenylpyridines and dihydrofuro[2,3-b]pyridines in moderate to high yields. This cascade reaction was completed within 30 min at room temperature, generating 1 equiv of H2O as the sole byproduct.

A novel Ir-catalyzed annulation of imidamides with sulfonyl azides has been developed. 1,2-Disubstituted benzimidazoles could be easily obtained in up to 99% yield for more than 40 examples. The products further streamline the synthesis of molecules that are important building blocks for organic synthesis and drug discovery. This strategy features high regioselectivity, efficiency, good tolerance of functional groups, and mild reaction conditions.

The Rh-catalyzed ortho-C–H carbenoid insertion reaction of diarylazines with diazo compounds has been developed. A wide range of ortho-substituted diarylazines have been obtained in moderate to high yields with high regioselectivity at room temperature. The hydrolysis of the products could release ketones or aldehydes, giving access to aromatic 1,5-keto-diesters as valuable synthons for further chemical transformations.

Picolinamide has first been employed as a traceless directing group for the cobalt-catalyzed oxidative annulation of benzylamides with alkynes to synthesize isoquinolines through C–H/N–H bonds activation. Oxygen is used as a terminal oxidant. This protocol exhibits good functional group tolerance and excellent regioselectivity. Both terminal and internal alkynes can be efficiently applied to this catalytic system as substrates.

A highly convergent one-pot synthesis of Hantzsch-type pyridines has been developed based on a three-component annulation of 1,3-dicarbonyl compounds, DMSO, and ammonium salt. A transition-metal-free oxidative methylenation reaction/Hantzsch pyridine synthesis cascade reaction was involved in this process. This intermolecular annulation reaction proceeds under mild reaction conditions, wherein DMSO serves as solvent, carbon source, and oxidant. A series of polysubstituted pyridines and methylene-bridged bis-1,3-dicarbonyl compounds were prepared in high yields.

An Ir(III)-catalyzed regioselective C–H amidation of anilines with sulfonyl azides is described. The developed protocol has good compatibility with diverse functional groups, efficiently providing the monoamidated products with good to excellent yields under mild reaction conditions. Furthermore, the 2-pyrimidyl and sulfonyl moieties in the amidated products can readily be removed, offering the synthetically useful 1,2-diaminobenzene scaffold.

The facile synthesis of various 1-aminoindoles from readily available aryl hydrazines, diazo compounds and ketones via rhodium catalysed C–H activation has been developed. The reaction was carried out under mild reaction conditions using hydrazone as a directing group, which was formed by the in situ condensation of hydrazines and ketones. This protocol exhibits a broad substrate scope and step economy, releasing N2 and H2O as the byproducts, obviating the need for external oxidants and pre-functionalized substrates.

AbstractArene homologation employing internal alkynes as coupling partners and 2-pyridyloxyl as directing group through dual C−H bond functionalization was accomplished using (pentamethylcyclopentadienyl)-rhodium(III) chloride dimer as a pre-catalyst. This protocol proved tolerant of synthetically valuable functional groups, and provided an expeditious access to highly congested naphthalene derivatives in moderate to good yields. Furthermore, the pyridyl moiety could be removed to furnish the versatile (OH)-free naphthols.

An efficient hydroamidation of benzylamides with internal alkynes catalyzed by Ru(II) has been developed. Various (E)-enamides were afforded in up to 95% yield for 28 examples. The protocol features excellent regio- and stereoselectivity, widely functional group tolerance, and easily accessible starting materials.Keywords: C−N formation; enamides; hydroamidation; interanl alkynes; ruthenium

A convenient “one-pot” regiospecific synthesis of substituted quinoxalines from o-phenylenediamines and ynones under metal-free conditions has been developed. An intermolecular Michael addition reaction, a dehydration condensation, and a base-promoted C-α-CH2-extrusion were involved in this procedure, which features high regioselectivity, efficiency, and environmental friendliness. Various quinoxalines were provided in up to 95% yield for 33 examples.

A direct C–H bond phosphonation of quinoxalin-2(1H)-ones with H-phosphonates, H-phosphinates or H-phosphine oxides has been developed. A wide variety of heteroaryl phosphonates were obtained in up to 92% yield for 20 examples under transition-metal-free conditions. This protocol tolerates a broad scope of substrates and features practicality, high efficiency, environmental friendliness and atom economy.

A novel protocol to synthesize multisubstituted benzo[b][1,4]oxazepines from N-(2-haloaryl)enaminones has been developed. In this procedure, only 2 equiv. of Cs2CO3 was required. A variety of polysubstituted benzo[b][1,4]oxazepine derivatives were provided in up to 95% yield for 27 examples.

Ir-catalyzed direct C–H sulfamidation of benzaldehydes has been achieved. A series of ortho-amided benzaldehydes were obtained in up to 95% yields for 21 examples with excellent regioselectivity and broad functional group tolerance. This transformation could proceed smoothly with low catalyst loading under external-oxidant-, acid-, or base-free conditions. Molecular nitrogen was released as the sole byproduct, providing an environmentally benign sulfamidation process.

A KOH-promoted regiospecific synthesis of polysubstituted N-(2-pyridyl)pyrroles under transition metal-free conditions has been developed. The pyrrole and pyridine rings were simultaneously installed from acyclic enaminone precursors under mild conditions and generated 1 equiv. of H2O as the sole byproduct. A series of polysubstituted N-(2-pyridyl)pyrroles were provided in up to 91% yield for 21 examples.

An efficient synthesis of C4-functionalized quinolines through copper-catalyzed tandem annulation of alkynyl imines with diazo compounds is described. This transformation involves an in situ formation of allene and intramolecular electrocyclization, which features high efficiency, mild reaction conditions, easy operation, and broad functional-group tolerance. A wide variety of C4-functionalized quinolines were provided in up to 92% yield for 33 examples.

An efficient, environmentally friendly, and operationally simple procedure to 1,2-disubstituted indoles from 2-alkynylanilines and diaryliodonium salts has been developed. This reaction proceeds smoothly under metal-free conditions. The products obtained could be transferred into 3,3′-diindolylmethane with DMSO catalyzed by palladium. The isotopic label experiments indicated that the methylene group in 3,3′-diindolylmethane is derived from DMSO. The diverse indoles were obtained in up to 90% yield for 28 examples.

A novel dehydrodimerization of malonates with indoles has been developed, providing simple and rapid access to 3-indolyl tetramethyl 1,1,2,2-ethanetetracarboxylates. Pd(OAc)2-catalyzed ‘one pot’ C(sp2)–C(sp3) and C(sp3)–C(sp3) cross-dehydrogenative-couplings of malonates with a variety of 2-aryl indoles were involved. The titled compounds were obtained in high yields with good functional group tolerance.

N-Pyridylation of various N-heteroarenes, including N-heteroarene-containing peptides, was achieved using N-propargyl enaminones (isolated or generated in situ from propargyl amine and propynones) as masked polysubstituted pyridine cores. This metal-free procedure proceeds under mild reaction conditions and generates 1 equiv of H2O as the sole byproduct.

An unprecedented practical access to 1,3,5-triarylbenzenes has been developed from chalcones with DMSO as a reaction partner and solvent. This procedure involved a base-promoted addition of dimethyl sulfoxide anion to chalcones, followed by an aldol-type cyclization. The results of the isotopic labeling experiments indicated that one C of the central benzene ring was derived from DMSO. In comparison to the reported methods of preparing triarylbenzenes, this protocol could simultaneously provide C3-symmetric and C3-unsymmetric triarylbenzenes under obviously milder reaction conditions (60 °C, 5 h). The diverse functionalized triarylbenzenes were obtained in up to 82% yields for 24 examples.

A convenient “one-pot” base-promoted synthesis of polysubstituted pyridines from 1-arylethylamines and ynones through the direct β-C(sp3)–H functionalization of enaminones under metal-free conditions has been developed. An intermolecular Michael addition reaction and an intramolecular condensation were involved in this procedure, which features high regioselectivity, high efficiency, and environmental friendliness. Various polysubstituted pyridines were provided in up to 92% yield for 34 examples.

A novel copper-catalyzed synthesis of quinazolinones from easily available 2-arylindoles and amines or ammoniums has been developed, which provided various quinazolinones in up to 99% yields for 43 examples. This strategy features tolerance of a wide range of functional groups, easily available starting materials, simple operation, mild reaction conditions, and environmental friendliness.

A novel and efficient approach to 3-allyl-chromones from alkynones and allylic alcohols via a tandem Michael addition–Claisen rearrangement–O-arylation reaction has been developed. Diversely structural 3-allyl-chromones were afforded in up to 93% yield for 24 examples. This synthetic strategy is regiospecific, highly efficient, environment friendly and metal-free.

A KI-catalyzed oxidative coupling of benzothiazoles with aryl aldehydes has been developed using TBHP as an oxidant in neat water under metal free conditions. Various 2-aryl benzothiazoles were prepared in 36–79% yields for 28 examples. The mechanistic studies suggested that this transformation proceeded via a radical process.

The homo-coupling of various terminal alkynes were realized in the presence of 0.5 mol% CuI and 5 mol% benzylamine. This transformation proceeded at room temperature under solvent and base free conditions using O2 as an oxidant. The TON was up to 1760.

We have developed a green and practical method to construct 4H-benzo[d][1,3]dioxin-4-one and its derivatives, which are important structural units in insecticides, and intermediates to synthesize multiple-substituted benzene derivatives of great value. The catalyst- and additive-free conditions, commercial and cheap starting materials and short reaction time, make this transformation practical and attractive.

An efficient “one-pot” approach to multiple substituted ureas from N-arylcyanamide and diaryliodonium salts has been presented. The two-step procedure involved the weak base-promoted chemoselective arylation of secondary amines with diaryliodonium and Cu-catalyzed nucleophilic addition of N-arylcyanamide with second diaryliodonium. The diverse unsymmetrical arylureas were obtained in up to 91% yield for 29 examples.

A general and efficient palladium-catalyzed oxidative cross-coupling reaction of N-tosylhydrazones with indoles providing N-vinylindoles has been developed. The reaction proceeds smoothly with various indoles and N-tosylhydrazones in a stereocontrolled manner, and a wide variety of N-vinylindoles were obtained up to 99% yields for 26 examples.

A novel and efficient approach to 4-sulfonamidoquinolines via copper-catalyzed cascade reaction of sulfonyl azides with alkynyl imines has been developed in which a 1,3-dipole cycloaddition/ketenimine formation/6π-electrocyclization/[1,3]-H shift cascade reaction was involved. Various 4-sulfonamidoquinolines were afforded in up to 84% yield for 19 examples. This synthetic strategy features with atom economy, concise steps, easy operation, and mild reaction conditions.

Dichloromethane (DCM) as a C1 source has been discovered: methylene diesters from DCM and carboxylic acids or aldehydes with TBHP in water were efficiently synthesized. The reactions proceed under mild conditions and afford both aliphatic and aromatic methylene diesters in good to excellent yields (up to >99%). 2-Chloroethyl benzoates and 3-chloropropyl benzoates are easily obtained in the same way from 1,2-dichloroethane and 1,3-dichloropropane, respectively, in good to excellent yields.

A redox-economic strategy has been developed, involved in an efficient Rh(III)-catalyzed oxidative C–H activation and alkyne annulation with perester as the oxidizing directing group. In this process, the cleavage of an oxidizing O–O bond as an internal oxidant is described for the first time. This reaction could be carried out under mild conditions and exhibits excellent regioselectivity and wide functional groups tolerance.

A KI-catalyzed oxidative coupling of benzothiazoles with aryl aldehydes has been developed using TBHP as an oxidant in neat water under metal free conditions. Various 2-aryl benzothiazoles were prepared in 36–79% yields for 28 examples. The mechanistic studies suggested that this transformation proceeded via a radical process.

A novel protocol to synthesize multisubstituted benzo[b][1,4]oxazepines from N-(2-haloaryl)enaminones has been developed. In this procedure, only 2 equiv. of Cs2CO3 was required. A variety of polysubstituted benzo[b][1,4]oxazepine derivatives were provided in up to 95% yield for 27 examples.

A direct C–H bond phosphonation of quinoxalin-2(1H)-ones with H-phosphonates, H-phosphinates or H-phosphine oxides has been developed. A wide variety of heteroaryl phosphonates were obtained in up to 92% yield for 20 examples under transition-metal-free conditions. This protocol tolerates a broad scope of substrates and features practicality, high efficiency, environmental friendliness and atom economy.

A novel and efficient approach to 3-allyl-chromones from alkynones and allylic alcohols via a tandem Michael addition–Claisen rearrangement–O-arylation reaction has been developed. Diversely structural 3-allyl-chromones were afforded in up to 93% yield for 24 examples. This synthetic strategy is regiospecific, highly efficient, environment friendly and metal-free.

A novel and environmentally benign protocol for diaryl-1,2-diketones was developed. Various diaryl-1,2-diketones were afforded in moderate to excellent yields by C–C triple bond cleavage of alkynones using molecular oxygen as an oxidant. A plausible reaction mechanism was proposed that accounts for all the experimental results. The products are important building blocks in organic synthesis and could be converted to various synthons via diverse transformations.