Rhodium(III)-Catalyzed Direct C-2 Olefination of Unactivated Indoles Utilizing OH/NH2as Directing Group

Cyanomethylation of the Benzene Rings and Pyridine Rings via Direct Oxidative Cross-Dehydrogenative Coupling with Acetonitrile

A novel and efficient approach for the amine-directed dehydrogenative C(sp²)-C(sp³) coupling of arylamines with acetonitrile was reported by using FeCl₂ as the catalyst. Substituted anilines, aminopyridines, naphthylamines, and some nitrogen-containing heterocyclic arylamines react with inactive acetonitrile to form the corresponding arylacetonitriles in moderate to good yields. This protocol features nontoxic iron catalysis, efficient atom economy, nonprefunctionalized starting materials, good regioselectivity, and excellent compatibility of functional groups and aromatic rings, providing a novel, straightforward, and green approach toward arylacetonitriles.

BN/BO-Ullazines and Bis-BO-Ullazines: Effect of BO Doping on Aromaticity and Optoelectronic Properties

We have achieved substitutional doping of ullazine with either two BO units or with one BO unit and one BN unit. The synthesis of these B-doped ullazines is straightforward, using demethylation and borylative cyclization as the key steps. Ullazine cores of both BN/BO-ullazines (2) and bis-BO-ullazines (3) are very close to being planar. Their electronic and photophysical properties were investigated by ultraviolet-visible, fluorescence spectroscopy, cyclic voltammetry, and density functional theory calculations.

Synthesis of Oxazino[4,3-a]indoles and biological applications

This review brings together the various pathways to the oxazino[4,3-a]indole motif over the last decades. Representative examples showing the scope of these processes will illustrate the synthetic pathways and the biological activity of the synthesized oxazinoindoles will be mentioned wherever possible.

An entry to 2-(cyclobut-1-en-1-yl)-1H-indoles through a cyclobutenylation/deprotection cascade

A transition-metal-free strategy for the synthesis of 2-(cyclobut-1-en-1-yl)-1H-indoles under mild conditions is described herein. A series of substituted 2-(cyclobut-1-en-1-yl)-1H-indoles are accessed by a one-pot cyclobutenylation/deprotection cascade from N-Boc protected indoles. Preliminary experimental and density functional theory calculations suggest that a Boc-group transfer is involved in the underlying mechanism.

RhIII -Catalyzed Double Dehydrogenative Coupling of Free 1-Naphthylamines with α,β-Unsaturated Esters

The Rh^III -catalyzed, consecutive double C-H oxidative coupling of free 1-naphthylamine and α,β-unsaturated esters through C-H/C-H and C-H/N-H bonds is reported. The one step reaction leads to the formation of biologically important alkylidene-1,2-dihydrobenzo[cd]indoles scaffolds. This efficient process is much more synthetically convenient and useful than others because the starting materials, such as 1-naphthylamine derivatives are readily available and the free amine serves as a directing group.

Weak Coordinating Carbonyl-Directed Rhodium(III)-Catalyzed C-H Activation at the C4-Position of Indole with Allyl Alcohols

A weakly coordinating carbonyl-directed coupling of allyl alcohols at the C-4 position of indole derivatives under the C-H activation conditions catalyzed by Rh(III) is reported. This results in alkylation at the C-4 position of indole derivatives exclusively. The obtained product forms a tricyclic derivative under aldol reaction conditions, which can be a potential precursor for synthesizing a few alkaloid molecules such as ergot, hapalindole alkaloids, and related heterocyclic compounds.

Direct oxidative coupling of N-acyl pyrroles with alkenes by ruthenium(ii)-catalyzed regioselective C2-alkenylation

Ruthenium(ii)-catalyzed oxidative coupling by C2-alkenylation of N-acyl pyrroles with alkenes has been described. The acyl unit was found to be an effective chelating group for the activation of aryl C-H bonds ortho to the directing group. The alkenylation reaction of benzoyl pyrroles occurred regioselectively at the C2-position of the pyrrole ring, without touching the benzene ring. The reaction provides exclusively monosubstituted pyrroles under the optimized conditions. Disubstituted pyrroles could be obtained using higher loadings of the ruthenium(ii)-catalyst and the additives.

Palladium-catalyzed regioselective C–H alkynylation of indoles with bromoalkynes in water

A palladium-catalyzed regioselective C(sp²)–H alkynylation between indoles and bromoalkynes in water has been developed, affording diverse functionalized 2-alkynylindoles in good yields.

Rhodium(iii)-catalyzed C–H activation at the C4-position of indole: switchable hydroarylation and oxidative Heck-type reactions of maleimides

A Rh(iii)-catalyzed C–H activation of indole at the C4-position leading to novel and switchable functionalization has been reported by employing a weakly co-ordinating COCF₃ group as a directing group.

NH2-Directed C-H Alkenylation of 2-Vinylanilines with Vinylbenziodoxolones

The first directing-group-mediated C-H alkenylation with alkenyl-λ³-iodanes as electrophilic alkene-transfer reagents has been developed. The application of free aromatic amines as challenging but synthetically valuable directing groups in combination with an Ir^III catalyst enabled the synthesis of highly desirable 1,3-dienes in excellent yields of up to 98% with high to perfect (Z,E) stereoselectivity. A broad substrate scope and further synthetic modifications are demonstrated.

Electronic Nature of Ketone Directing Group as a Key To Control C-2 vs C-4 Alkenylation of Indoles

A novel mode of achieving site selectivity between C-2 and C-4 positions in the indole framework by altering the property of the ketone directing group is disclosed. Methyl ketone, as directing group, furnishes exclusively C-2 alkenylated product, whereas trifluoromethyl ketone changes the selectivity to C-4, indicating that the electronic nature of the directing group controls the unusual choice between a 5-membered and a 6-membered metallacycle. The screening of other carbonyl-derived directing groups reveals that strong and weak directing groups exhibit opposite selectivity. Experimental controls and deuteration experiments lend support to the proposed mechanism.

Oxidative Furan-to-Indole Rearrangement. Synthesis of 2-(2-Acylvinyl)indoles and Flinderole C Analogues

Oxidative rearrangement of 2-(2-aminobenzyl)furans affording 2-(2-acylvinyl)indoles in a stereocontrolled manner in good-to-excellent yields has been developed. Thus, (2-aminobenzyl)furans with electron-releasing alkoxy substituents in the phenyl group form only E-isomers of 2-(2-acylvinyl)indoles. Conversely, substrates without such substituents produce target products as Z-isomers exclusively. A short diastereoselective method for the transformation of the obtained 2-(2-acylvinyl)indoles into antimalarial bisindole alkaloid flinderole A-C analogues has been developed.

Manganese catalyzed C–H functionalization of indoles with alkynes to synthesize bis/trisubstituted indolylalkenes and carbazoles: the acid is the key to control selectivity

The Mn-catalyzed C–H alkenylations of indole with terminal- and/or internal-alkynes have been developed to selectively yield indolylalkene and carbazole.