Rh(III)-Catalyzed [4 + 2] Annulation of Indoles with Diazo Compounds: Access to Pyrimido[1,6-a]indole-1(2H)-ones

Gold-catalyzed C5-alkylation of indolines and sequential oxidative aromatization: access to C5-functionalized indoles

A novel protocol towards the rapid assembly of C5-alkylated indole derivatives has been developed via gold-catalyzed regioselective functionalization and subsequent oxidative aromatization.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.

Synthesis of [5,6]-Bicyclic Heterocycles with a Ring-Junction Nitrogen Atom: Rhodium(III)-Catalyzed C-H Functionalization of Alkenyl Azoles

The first syntheses of privileged [5,6]-bicyclic heterocycles, with ring-junction nitrogen atoms, by transition metal catalyzed C-H functionalization of C-alkenyl azoles is disclosed. Several reactions are applied to alkenyl imidazoles, pyrazoles, and triazoles to provide products with nitrogen incorporated at different sites. Alkyne and diazoketone coupling partners give azolopyridines with various substitution patterns. In addition, 1,4,2-dioxazolone coupling partners yield azolopyrimidines. Furthermore, the mechanisms for the reactions are discussed and the utility of the developed approach is demonstrated by iterative application of C-H functionalization for the rapid synthesis of a patented drug candidate.

Rhodium-catalyzed malonation of 2-arylquinazolines with 2-diazomalonates: double C–H functionalization

Herein, rhodium-catalyzed malonation of 2-arylquinazolines with diazomalonates was described.

An Ir(iii)-catalyzed aryl C–H bond carbenoid functionalization cascade: access to 1,3-dihydroindol-2-ones

An Ir(iii)-catalyzed relay aryl C–H bond carbenoid insertion cascade of N-aryl-2-pyridinamines with diazo Meldrum's acid has been developed.

Rhodium-catalyzed C2 and C4 C–H activation/annulation of 3-(1H-indol-3-yl)-3-oxopropanenitriles with internal alkynes: a facile access to substituted and fused carbazoles

Rhodium-catalyzed C2 and C4 C–H activation/annulation of 3-(1H-indol-3-yl)-3-oxopropanenitriles with internal alkynes has been developed. Substituted and fused carbazole derivatives were obtained through formal rhodium-catalyzed (4+2) or tandem (4+2) and (5+2) cycloaddition reactions under mild reaction conditions in good yields.

Synthesis of oxindole from acetanilide via Ir(iii)-catalyzed C–H carbenoid functionalization

The Ir(iii)-catalyzed intermolecular C–H annulations of acetanilide with diazotized Meldrum's acid furnished the oxindole derivative. Brief synthetic applications of the synthesized oxindole were also demonstrated.

Regio-selective synthesis of diversely substituted benzo[a]carbazoles through Rh(iii)-catalyzed annulation of 2-arylindoles with α-diazo carbonyl compounds

A novel synthetic approach toward benzo[a]carbazoles and 6-aminobenzo[a]carbazoles containing an unprotected NH unit through Rh(iii)-catalyzed cascade reactions of 2-arylindoles or 2-arylindole-3-carbonitriles with α-diazo carbonyl compounds is presented.

Highly fluorescent 1,2-dihydropyrimido[1,6-α]indole: an efficient metal free synthesis and photophysical study

A metal free route to highly fluorescent 1,2-dihydropyrimido[1,6-α]indole derivatives has been developed via base catalyzed aldol followed by the Mannich reaction of indole-2-carboxaldehyde with ethyl N-arylideneglycinate at room temperature. This transformation consists of the sequential formation of two new bonds to afford highly functionalized pyrimidoindole derivatives under mild reaction conditions. Photophysical properties of the products have also been reported.

Rhodium-catalyzed C–H activation of 3-(indolin-1-yl)-3-oxopropanenitriles with diazo compounds and tandem cyclization leading to hydrogenated azepino[3,2,1-hi]indoles

Rh(iii)-Catalyzed C–H activation of 3-(indolin-1-yl)-3-oxopropanenitriles with diazo compounds and tandem cyclization leading to seven-membered ring scaffolds has been developed.