Ring-opening formal hetero-[5+2] cycloaddition of 1-tosyl-2,3-dihydro-1H-pyrroles with terminal alkynes: entry to 1-tosyl-2,3-dihydro 2,3-dihydro-1H-azepines.

A new Lewis acid catalysed formal hetero-[5+2] cycloaddition of 2,3-dihydro-1H-pyrroles to terminal alkynes is described. By employing a FeCl3 and BF3·OEt2 co-catalytic strategy, the ring-opening of 1-tosyl-2,3-dihydro-1H-pyrroles by selective cleavage of the C(sp2)-N bond and subsequent annulation have been achieved to access 1-tosyl-2,3-dihydro-1H-azepines with excellent regioselectivity, offering a new avenue for cycloaddition through the ring-opening of non-strained-ring-based units.

Rhodium(III)-catalyzed oxidative bicyclization of 4-arylbut-3-yn-1-amines with internal alkynes through C-H functionalization.

A new Rh(iii)-catalyzed oxidative bicyclization through C-H functionalization is presented. This reaction allows the selective assembly of diverse benzo[g]indoles from 4-arylbut-3-yn-1-amines and internal alkynes via a sequence of aromatic C(sp(2))-H functionalization, cyclodimerization and nucleophilic cyclization.

Rhodium(III)-Catalyzed [3+2]/[5+2] Annulation of 4-Aryl 1,2,3-Triazoles with Internal Alkynes through Dual C(sp2)-H Functionalization.

A rhodium(III)-catalyzed [3+2]/[5+2] annulation of 4-aryl 1-tosyl-1,2,3-triazoles with internal alkynes is presented. This transformation provides straightforward access to indeno[1,7-cd]azepine architectures through a sequence involving the formation of a rhodium(III) azavinyl carbene, dual C(sp(2))-H functionalization, and [3+2]/[5+2] annulation.

Copper-catalyzed cascade cyclization of 1,7-enynes with aromatic sulfonyl chlorides toward selective assembly of benzo[j]phenanthridin-6(5H)-ones.

A step-economical method for the cascade cyclization of 1,7-enynes with aromatic sulfonyl chlorides by using a low-cost and more abundant Cu catalyst is presented. This method allows access to benzo[j]phenanthridin-6(5H)-ones and represents a new Cu-catalyzed cascade cyclization of 1,n-enynes.

Rhodium(III)-catalyzed [3+2] annulation of 5-aryl-2,3-dihydro-1H-pyrroles with internal alkynes through C(sp²)-H/alkene functionalization.

This study describes a new rhodium(III)-catalyzed [3+2] annulation of 5-aryl-2,3-dihydro-1H-pyrroles with internal alkynes using a Cu(OAc)2 oxidant for building a spirocyclic ring system, which includes the functionalization of an aryl C(sp(2))-H bond and addition/protonolysis of an alkene C=C bond. This method is applicable to a wide range of 5-aryl-2,3-dihydro-1H-pyrroles and internal alkynes, and results in the assembly of the spiro[indene-1,2'-pyrrolidine] architectures in good yields with excellent regioselectivities.

Palladium-catalyzed oxidative difunctionalization of alkenes with α-carbonyl alkyl bromides initiated through a Heck-type insertion: a route to indolin-2-ones.

The oxidative interception of various σ-alkyl palladium(II) intermediates with additional reagents for the difunctionalization of alkenes is an important research area. A new palladium-catalyzed oxidative difunctionalization reaction of alkenes with α-carbonyl alkyl bromides is described, in which the σ-alkyl palladium(II) intermediate is generated through a Heck insertion and trapped using an aryl C(sp(2))-H bond. This method can be applied to various α-carbonyl alkyl bromides, including primary, secondary, and tertiary α-bromoalkyl esters, ketones, and amides.

Hexafluoroantimonic acid catalysis: formal [3+2+2] cycloaddition of aziridines with two alkynes.

A practical method for the synthesis of azepine derivatives, a typical seven-membered heterocyclic ring system, was developed and involves the use of hexafluoroantimonic acid to catalyze a formal [3+2+2] cycloaddition of aziridines with two alkynes. This method was applicable to two of the same or different terminal alkynes for the [3+2+2] cycloaddition with unactivated aziridines, and furnished the corresponding azepine derivatives in good yields with good levels of chemo- and regioselectivity. The mechanism was also discussed according to the results of the in situ HRMS and (1)H NMR analysis.

Alkylation of terminal alkynes with transient σ-alkylpalladium(II) complexes: a carboalkynylation route to alkyl-substituted alkynes.

A mild and general alkylation of terminal alkynes with transient σ-alkylpalladium(II) complexes for assembling alkyl-substituted alkynes is described. This method represents a new way to the use of transient σ-alkylpalladium(II) complexes in organic synthesis through 1,2-carboalkynylation of alkenes.

Oxidative 1,2-difunctionalization of activated alkenes with benzylic C(sp3)-H bonds and aryl C(sp2)-H bonds.

DTBP (di-tert-butyl peroxide) is utilized to mediate oxidative 1,2-difunctionalization of activated alkenes with an aryl C(sp(2))-H bond and a benzylic C(sp(3))-H bond for the synthesis of functionalized oxindoles. This reaction is a new organomediated strategy for alkene difunctionalization facilitated by Lewis acids.

Synthesis of 3-(aminomethylene)-2-oxoindolines by palladium-catalyzed annulation of 3-chloro-2-iodo-N-arylacrylamides with amides or amines.

A new palladium-catalyzed C-H bond activation-annulation-amination tandem method was presented for selectively synthesizing 3-(aminomethylene)-2-oxoindolines. In the presence of Pd(dba)(2), xantphos (L8), AgOAc and Na(2)CO(3), a variety of 3-chloro-2-iodo-N-arylacrylamides underwent the reaction with amides or amines to afford the corresponding 3-(aminomethylene)-2-oxoindolines in moderate to good yields.

Iron-mediated [3 + 2] or [3 + 3] annulation of 2-(2-(ethynyl)phenoxy)-1-arylethanones: selective synthesis of indeno[1,2-c]chromenes and 5H-naphtho[1,2-c]chromenes.

An iron-mediated tandem annulation strategy has been developed for the synthesis of numerous functional indeno[1,2-c]chromenes and 5H-naphtho[1,2-c]chromenes. This work is the first to disclose an iron-mediated method through sequential electrophilic addition of a ketone to an alkyne and annulation tandem reaction. Importantly, a halide is introduced into the products by a ring-opening process among the annulation of alkynylcyclopropanes, which makes the methodology more attractive for organic synthesis.

Palladium-catalyzed cross-coupling of electron-poor terminal alkynes with arylboronic acids under ligand-free and aerobic conditions.

Palladium-catalyzed cross-coupling reaction of terminal alkynes with arylboronic acids has been described. In the presence of Pd(OAc)(2) and Ag(2)O, a variety of terminal alkynes, including electron-poor terminal alkynes, smoothly underwent the reaction with numerous boronic acids to afford the corresponding internal alkynes in moderate to good yields. Moreover, this methodology was applied to the synthesis of 1H-isochromenes and diynes. It is noteworthy that the reaction proceeds under ligand-free and relative lower loading Pd conditions, and the maximal TONs (turnover numbers) of the reaction are up to 720,000.

Copper-catalyzed intramolecular C-H oxidation/acylation of formyl-N-arylformamides leading to indoline-2,3-diones.

A new, efficient Cu-catalyzed intramolecular C-H oxidation/acylation method has been developed for the synthesis of substituted indoline-2,3-diones (isatins). In the presence of CuCl(2) and O(2), a variety of formyl-N-arylformamides underwent the tandem reaction to afford the corresponding indoline-2,3-diones in moderate to good yields. It is noteworthy that the reaction serves as the first example of transition-metal-catalyzed transformation for the preparation of indoline-2,3-diones.

Iron-catalyzed annulations of 2-(2-alkynyl)phenoxy)-1-arylethanones leading to substituted naphthalen-1-ols.

A novel intramolecular annulation of 1-(2-alkynylphenoxy)propan-2-ones catalyzed by iron, an economical and environmentally-benign transition metal, has been developed; this new atom-economical route includes dual C-H functionalizations to construct the naphthalen-1-ol or anthracen-1-ol skeletons.