Rhodium(III)-Catalyzed CH Activation of Arenes Using a Versatile and Removable Triazene Directing Group

Triazenyl Alkynes as Versatile Building Blocks in Multicomponent Reactions: Diastereoselective Synthesis of β-Amino Amides

Multicomponent reactions (MCRs) are powerful tool for the construction of polyfunctional molecules in an operationally simple and atom-economic manner, and the discovery of novel MCRs requests various building blocks. Herein, triazenyl alkynes were disclosed as versatile building blocks in a multicomponent reaction with carboxylic acids, aldehydes and anilines to furnish β-amino amides with the achievement of high diastereoselectivity and structural diversity. In this process, triazenyl alkynes were bifunctional so that the alkyne moiety acts as C2 fragment and triazene serves as directing group to modulate the transition state thus achieving high diastereoselectivity, in consistence with DFT calculations. Furthermore, the triazenyl group also enables diverse late-stage transformation. This protocol opens a new vision for the discovery of building block and rational design of MCRs.

Vinyl and Alkynyl Triazenes: Synthesis, Reactivity, and Applications

Aromatic compounds containing triazenyl groups (N₃ RR') have a profound impact on synthetic organic and medicinal chemistry. In contrast, the chemistry of vinyl and alkynyl triazenes was a largely uncharted territory until recently. The situation has changed over the last five years, and it has become apparent that vinyl and alkynyl triazenes are highly interesting compounds with a unique reactivity. The electron-donating properties of the triazenyl group provide alkynyl triazenes with an ynamide-like reactivity, which can be exploited in reactions of the triple bond. Vinyl triazenes, on the other hand, can be used for electrophilic vinylation reactions. The foundation for this new triazene chemistry are synthetic pathways which allow preparing vinyl and alkynyl triazenes in few steps from readily available starting materials. In this Minireview, we summarize recent developments in this area.

A One-Pot Ring-Opening/Ring-Closure Sequence for the Synthesis of Polycyclic Spirooxindoles

One-pot ring-opening/ring-closure process of combining methyleneindolinone with 3-aminooxindole has been developed in this work. Novel polycyclic spirooxindoles were efficiently assembled under mild conditions in high yields (up to 95 %) with moderate to good diastereoselectivities (up to >95:5 d.r.) through simple filtration.

Cationic Cobalt(III) Catalyzed Indole Synthesis: The Regioselective Intermolecular Cyclization of N-Nitrosoanilines and Alkynes

The unique regioselectivity and reactivity of cobalt(III) in the direct cyclization of N-nitrosoanilines with alkynes for the expedient synthesis of N-substituted indoles is demonstrated. In the presence of a cobalt(III) catalyst, high regioselectivity was observed when using unsymmetrical meta-substituted N-nitrosoanilines. Moreover, internal alkynes bearing electron-deficient groups, which are almost unreactive in the [Cp*Rh(III)]-catalyzed system, display good reactivity in this transformation.

Relayed Regioselective Alkynylation/Olefination of Unsymmetrical Cyclic Diaryliodonium Species Catalyzed by Cu and Pd: Affording Fluorescent Cytotoxic Benzoxazoles

Although cyclic diaryliodonium species have the potential to act as valuable synthons for cascade transformations, they still remain largely unexplored. The regioselectivity associated with unsymmetrical cyclic diaryliodonium species has previously been known to pose a challenge. A regioselective relayed alkynylation and olefination of unsymmetrical cyclic diaryliodonium species has been achieved by installation of a directing amido group. These relayed transformations were delayed until an oxazole ring had formed, delivering a series of unique fluorescent benzoxazoles. Moreover, some of these synthetic benzoxazoles showed apparent inhibitory activity against malignant cancer cells. Further confocal visualization revealed that benzoxazoles targeted cell nuclei. These findings might provide a novel structural scaffold to develop desirable anticancer agents.

Rhodium(III)-catalyzed cyclative capture approach to diverse 1-aminoindoline derivatives at room temperature

A Rh(III) -catalyzed C-H activation/cyclative capture approach, involving a nucleophilic addition of C(sp(3) )-Rh species to polarized double bonds is reported. This constitutes the first intermolecular catalytic method to directly access 1-aminoindolines with a broad substituent scope under mild conditions.

Synthesis of triazenes with nitrous oxide

Triazenes are valuable compounds in organic chemistry and numerous applications have been reported. Furthermore, triazenes have been investigated extensively as potential antitumor drugs. Here, we describe a new method for the synthesis of triazenes. The procedure involves a reagent which is rarely used in synthetic organic chemistry: nitrous oxide (N2 O, "laughing gas"). Nitrous oxide mediates the coupling of lithium amides and organomagnesium compounds while serving as a nitrogen donor. Despite the very inert character of nitrous oxide, the reactions can be performed in solution under mild conditions. A key advantage of the new procedure is the ability to access triazenes with alkynyl and alkenyl substituents. These compounds are difficult to prepare by conventional methods because the required starting materials are unstable. Some of the new alkynyltriazenes were found to display high cytotoxicity in in vitro tests on ovarian and breast cancer cell lines.

Unique regioselectivity in the C(sp3)-H α-alkylation of amines: the benzoxazole moiety as a removable directing group

The benzoxazol-2-yl- substituent was found to act as a removable activating and directing group in the Ir-catalyzed alkylation of C(sp(3))-H bonds adjacent to nitrogen in secondary amines. It can be easily introduced by oxidative coupling or by an SNAr reaction, and it can be removed by hydroxide or by hydride reduction. For 1,2,3,4-tetrahydroisoquinolines, activation exclusively takes place in the 3-position. A variety of activated as well as unactivated terminal olefins are suitable reaction partners.