Rhodium(III)-Catalyzed Dehydrogenative Heck Reaction of Salicylaldehydes

Convergent Synthesis of Diverse Nitrogen Heterocycles via Rh(III)-Catalyzed C-H Conjugate Addition/Cyclization Reactions

The development of Rh(III)-catalyzed C-H conjugate addition/cyclization reactions that provide access to synthetically useful fused bi- and tricyclic nitrogen heterocycles is reported. A broad scope of C-H functionalization substrates and electrophilic olefin coupling partners is effective, and depending on the nature of the directing group, cyclic imide, amide, or heteroaromatic products are obtained. An efficient synthesis of a pyrrolophenanthridine alkaloid natural product, oxoassoanine, highlights the utility of this method.

Copper-catalyzed cascade annulation of unsaturated α-bromocarbonyls with enynals: a facile access to ketones from aldehydes

A Cu-catalyzed cascade annulation of enynals with alkenyl or alkynyl α-bromocarbonyls for the synthesis of various cyclohexenone-fused polycyclic compounds is described. Up to six new C-C bonds and four new carbocycles can be established in a single reaction, highlighting the high efficiency and step-economics of this protocol. This reaction offers a novel and straightforward entry to the synthesis of ketones featuring the addition of carbon radicals to aldehydes.

Individual and combined antiparasitic effect of six plant metabolites against Leishmania amazonensis and Trypanosoma cruzi

Six plant metabolites including isobavachalcone (1), 4-hydroxylonchocarpine (2), and (E)-1-(2,2-dimethyl-2H-chromen-6-yl)-3-(4-hydroxyphenyl)prop-2-en-1-one (3), 6,8-(di-3-methyl-but-2-enyl)eriodictyol (4), damnacanthal (5), and buesgenine (6) were evaluated for their leishmanicidal and trypanocidal activities against intracellular amastigotes of Leishmania amazonensis and Trypanosoma cruzi. Compounds 2-4 and 6 displayed antileishmanial activity while 3 and 5 showed trypanocidal effect. The leishmanicidal activity of 6 was expressed with the lowest IC50 (5.70μg/mL) whereas the most trypanocidal metabolite (5) showed its activity with IC50 at 11.14μg/mL. In addition, antiprotozoal effect of mixtures of 1-6 prepared at different ratios (3:1, 1:1, and 1:3) was also investigated. Interestingly, 1 and 2 initially inactive against T. cruzi, displayed trypanocidal activities when mixed together. This activity increased when 3 (13.63μg/mL) was combined with 1 in ratios 1:1 (10.01μg/mL) and 3:1 (7.78μg/mL). Moreover, the leishmanicidal effect of 4 against L. amazonensis increased in the mixture 6/4 (1:3).

Iridium- and rhodium-catalyzed C–H activation and formyl arylation of benzaldehydes under chelation-assistance

Mild and efficient synthesis of benzophenones via Ir(iii)- and Rh(iii)-catalyzed, directing group-assisted formyl C–H arylation of benzaldehydes has been achieved using diaryliodonium salts, in which Rh(iii) and Ir(iii) catalysts exhibited a complementary substrate scope.

Rhodium(iii)-catalyzed C–C coupling of 7-azaindoles with vinyl acetates and allyl acetates

The behaviour of electron-rich alkenes with 7-azaindoles in rhodium(iii)-catalyzed C–H activation is investigated.

Rh-catalyzed direct synthesis of 2,2′-dihydroxybenzophenones and xanthones

An efficient rhodium-catalyzed direct synthesis of 2,2′-dihydroxybenzophenones and xanthones was developed from functionalized salicylaldehydes.

Highly efficient dehydrogenative cross-coupling of aldehydes with amines and alcohols

A common protocol for the synthesis of amides, esters and α-ketoesters via cross dehydrogenative coupling of aldehydes and amines/alcohols has been developed.

Oxidant controlled regioselective mono- and di-functionalization reactions of coumarins

C-3 alkylation of coumarins has been accomplished using cycloalkanes/alkylbenzenes and Fe^III/DTBP while C-4 cycloalkylation–C-3 peroxidation has been achieved using AcOH/TBHP.

Rh(iii)- or Ir(iii)-catalyzed ynone synthesis from aldehydes via chelation-assisted C–H bond activation

A simple and practical synthesis of ynones directly from readily available aldehydes was developed for the first time under mild reaction conditions via a Rh(iii)- or Ir(iii)-catalyzed formyl C–H bond activation.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

In this review, a summary of transition metal-catalyzed C–H activation by utilizing the functionalities as directing groups is presented.

Pd(OAc)2/SPPh3 accelerated activation of gem-dichloroalkenes for the construction of 3-arylchromones

The Pd-catalyzed regioselective intramolecular nucleophilic substitution of gem-dichloroalkene derivatives with salicylaldehydes leading to the synthesis of 3-arylchromones has been developed.

Synthesis of indoles and polycyclic amides via ruthenium(ii)-catalyzed C–H activation and annulation

Ruthenium(ii)-catalyzed oxidative coupling of NH protic amides with alkynes has been developed for the synthesis of a diversity of complex structures, such as N-acyl indole and tricyclic amide derivatives.

Vanadyl species-catalyzed complementary β-oxidative carbonylation of styrene derivatives with aldehydes

By judicious choice of the counter anions in the vanadyl catalysts, we can achieve β-hydroxylated and t-butyl peroxylated carbonylation of styrenes by aromatic 1° and 2° alkyl aldehydes in a complementary manner.

A complete switch of the directional selectivity in the annulation of 2-hydroxybenzaldehydes with alkynes

Controlling reaction selectivity is an eternal pursuit for chemists working in chemical synthesis. As part of this endeavor, our group has been exploring the possibility of constructing different natural product skeletons from the same simple starting materials by using different catalytic systems. In our previous work, an isoflavanone skeleton was obtained from the annulation of a salicylaldehyde and an alkyne when a gold catalyst was employed. In this paper, it is shown that a coumarin skeleton can be efficiently obtained through an annulation reaction with the same starting materials, that is, terminal alkynes and salicylaldehydes, by simply switching to a rhodium catalyst. A plausible reaction mechanism is proposed for this new annulation based on isotopic substitution experiments.

A multitasking functional group leads to structural diversity using designer C-H activation reaction cascades

The C-H activation strategy has become one of the preferred methods to introduce chemical functionality to a chemically inert carbon atom. Intensive efforts have been devoted to developing either versatile bond formations (product structural diversity) or effective directing groups (substrate site selectivity). From the views of medicinal and synthetic practitioners, the C-H activation approach remains inadequate due to its limitation to point-to-point derivatization. Direct assembly of 3D molecular complexity in a single step remains elusive for this strategy. Towards this goal, a multitasking functional group is required to accomplish several missions in one pot: site selecitivity, cleavability and redox versatility. We demonstrate that an oxyacetamide group is such a multifunctional warhead that enables a series of C-H functionalization cascades and allows direct access to structurally diverse polycyclic heterocyles in one pot. The progress of these reaction cascades were fully controlled by oxidants and temperature. The proliferation of the reaction chain can be extended to a four-step cascade.

Ru-catalyzed branched versus linear selective C3-alkylation of 2-aroylbenzofurans with acrylates via C-H activation

The carbonyl-directed C3-H activation and alkylation of 2-aroylbenzo[b]furans with acrylates occurs selectively either in a linear or branched fashion, depending on the catalyst employed; [Ru(p-cymene)Cl2]2 or Ru(PPh3)3Cl2, respectively. Two alternate pathways--funded upon the differences in steric and electronic preferences of these two complexes--is proposed for the selectivity of linear versus branched products.