Pyridine Activation via Copper(I)-Catalyzed Annulation toward Indolizines

Cyclopentene Annulations of Alkene Radical Cations with Vinyl Diazo Species Using Photocatalysis

A direct (3+2) cycloaddition between alkenes and vinyl diazo reagents using either Cr or Ru photocatalysis is described. The intermediacy of a radical cation species enables a nucleophilic interception by vinyl diazo compounds, a departure from their traditional electrophilic behavior. A variety of cyclopentenes are synthesized using this method, and experimental insights implicate a direct cycloaddition instead of a cyclopropanation/rearrangement process.

Silver-catalyzed regioselective hydroamination of alkenyl diazoacetates to synthesize γ-amino acid equivalents

A simple protocol to directly access γ-amino acid derivatives by intermolecular regioselective hydroamination of trichloroethyl alkenyldiazoacetates with carbamate using a silver tetrafluoroborate catalyst is described. Density functional theory (DFT) calculations to analyze the reaction mechanism revealed that multiple attractive interactions occur in a transition state to promote the vinylogous addition of nitrogen nucleophiles.

Catalytic vinylogous cross-coupling reactions of rhenium vinylcarbenoids

We report the first example of the rhenium-catalyzed allylation reaction of indolyl compounds by means of cross-coupling with propargyl ethers as non-obvious allylating reagents.

We report the first example of the rhenium-catalyzed allylation reaction of indolyl compounds by means of cross-coupling with propargyl ethers as non-obvious allylating reagents. Data from isotope-labeling and kinetic isotopic studies are consistent with a mechanism that proceeds by vinylidene formation as the rate determining step, followed by 1,5-hydride shift to generate a key rhenium vinylcarbenoid complex. Bond formation occurs at the vinylogous site and the reaction is conveniently carried out in air.

Copper-catalyzed [3 + 2 + 1] annulation for functionalized pyridines as potent and dynamic UV absorbers

A novel synthesis of functionalized pyridines via copper-catalyzed [3 + 2 + 1] annulation for the development of potent UV absorbers is described.

Catalyst-free [3 + 2] cyclization of dihydroisoquinoline imines and isatin-derived Morita–Baylis–Hillman carbonates via 1,5-electrocyclization: synthesis of tetrahydroisoquinoline-fused spirooxindoles

The incorporation of tetrahydroisoquinoline and spirooxindole frameworks has been achieved.

Synthesis of indolizine derivatives containing eight-membered rings via a gold-catalyzed two-fold hydroarylation of diynes

A novel strategy for a gold(i)-catalyzed synthesis of indolizine derivatives containing eight-membered rings has been developed, which may have potential usefulness as blue or green OLEDs.

One-Pot Synthesis of Indolizines via Sequential Rhodium-Catalyzed [2 + 1]-Cyclopropanation, Palladium-Catalyzed Ring Expansion, and Oxidation Reactions from Pyridotriazoles and 1,3-Dienes

An efficient, one-pot synthetic method for producing functionalized indolizine derivatives was developed via a Rh-catalyzed [2 + 1]-cyclopropanation, Pd-catalyzed ring expansion, and subsequent oxidation using manganese dioxide from pyridotriazoles and 1,3-dienes.

Synthesis of azasilacyclopentenes and silanols via Huisgen cycloaddition-initiated C-H bond insertion cascades

An unusual transition metal-free cascade reaction of alkynyl carbonazidates was discovered to form azasilacyclopentenes. Mild thermolysis afforded the products via a series of cyclizations, rearrangements, and an α-silyl C-H bond insertion (rather than the more common Wolff rearrangement, 1,2-shift, or β-silyl C-H insertion) to form silacyclopropanes. A mechanistic proposal for the sequence was informed by control experiments and the characterization of reaction intermediates. The substrate scope and post-cascade transformations were also explored.

Indium(III)-catalyzed Aza-Conia-Ene Reaction for the Synthesis of Indolizines

A new indium(III)-catalyzed reaction for the synthesis of a series of indolizine scaffolds has been developed. This methodology was highly efficient, allowing a low catalyst loading of 2 mol % (down to 0.5 mol %) and rendering the products in high yields through a 5-exo-dig aza-Conia-ene reaction. Furthermore, the possibility of incorporating an electrophile into the generated pyrrolidone ring in a one-pot synergistic fashion was demonstrated. Finally, based on experimental observations, a mechanism proposal was outlined.

Metal-Free Cascade Approach toward Polysubstituted Indolizines from Chromone-Based Michael Acceptors

An efficient cascade transformation toward indolizine-based molecules has been developed. This process leads to the rapid construction of two C-N bonds and one C-C bond without the need of any metal catalysis. The approach involves easily accessible chromone-based Michael acceptors and propargylamine derivatives as starting materials. This cascade constitutes a novel and very competitive alternative to the well reported strategies using pyridine or pyrrole derivatives for accessing the indolizine ring with substituents at uncommon C-positions.

Chloroacetate Promotes and Participates in the Oxidative Annulation of Pyridines/Isoquinoline by Using Oxygen as the Oxidant

The aerobic oxidative annulation of chalcones, pyridines/isoquinoline and ethyl chloroacetate to indolizines was achieved by cascade reaction. Various functional groups on chalcones were tolerated. And different pyridines derivatives could also be suitable substrates. Ethyl chloroacetate is an essential component in participating of the oxidative annulation process. Overall, this protocol is very practical and efficient by using molecular oxygen as oxidant with high selectivity for the annulation product.

Recent Developments in Coinage Metal Catalyzed Transformations of Stabilized Vinyldiazo Compounds: Beyond Carbenic Pathways

Transition metal-catalyzed transformations of vinyldiazo compounds have become a versatile tool in organic synthesis. Although several transition metals have been investigated for this purpose, this field has been mainly dominated by dirhodium catalysts. Remarkable levels of chemo-, regio-, diastereo- and enantioselectivity have been reached in some of these rhodium-catalyzed transformations. In the last few years coinage metals have also emerged as useful catalysts in transformations involving vinyldiazo compounds. In some cases, highly efficient catalyst-dependent protocols arising from divergent mechanistic pathways have been reported. In this Personal Account, we aim to showcase recent advances in metal coinage catalyzed transformations of vinyldiazoacetates, an exciting field of research to which our group has actively contributed in the last few years.

How Dirhodium Catalyst Controls the Enantioselectivity of [3 + 2]-Cycloaddition between Nitrone and Vinyldiazoacetate: A Density Functional Theory Study

The origin of enantioselectivity in the dirhodium-catalyzed [3 + 2]-cycloaddition of nitrone and vinyldiazoacetate has been investigated using dispersion-corrected density functional theory. Taking a more realistic account of bulky ligands in models of the dirhodium catalyst when investigating its catalytic behavior is crucial for describing the effects resulting from a high level of asymmetric induction. More than one active site can be located and the extra reactivity is provided by an electron-donation interaction between the substrate and an additional Rh2L4 catalyst.

Multicomponent syntheses of functional chromophores

Multicomponent reactions are a valuable tool for the synthesis of functional π-electron systems. Two different approaches can be taken into account for accessing the target structures. In the more conventional scaffold approach an already existing chromophore is coupled with other components to give a complex functional π-system. Here, electronically monotonous components can also be introduced, which may exert synergistic electronic effects within the novel compound. The more demanding chromophore concept generates a complete π-electron system and a scaffold concurrently. The latter approach is particularly stimulating for methodologists since π-systems might be accessible from simple starting materials. This review encompasses the advances in the preparation of functional π-electron systems via multicomponent processes during the past few years, based both on the scaffold and chromophore concepts. Besides the synthetic strategies the most important properties, i.e. redox potentials, absorption and emission maxima or fluorescence quantum yields, of the synthesized molecules are highlighted.

A Cu-catalyzed four-component cascade reaction to construct β-ester-γ-amino ketones

Herein, a novel Cu-catalyzed four-component cascade reaction, which encompasses styrenes, diazo reagents, amines, and tert-butyl hydroperoxide (TBHP), was well developed toward β-ester-γ-amino ketones, which showed high chemoselectivity.

Recent advances in the synthesis of indolizines and their π-expanded analogues

Synthesis of indolizines developed during the last decade is reviewed, with special emphasis given to densely functionalized architectures, breakthrough strategies, compounds bearing electron-donating and electron-withdrawing substituents and π-expanded systems.

Synthesis, Characterization and Photophysical Properties of Naphtho[2,3-b]Indolizine-6,11-Dione Derivatives

This communication concerns the synthesis, structural characterization and fluorescent properties of novel naphtho[2,3-b]indolizine-6,11-dione derivatives. The target compound synthesized by one-pot multicomponent reaction between naphthoquinone, indandione and pyridine derivatives.The structures of synthesized compounds were characterized by IR, 1H NMR and 13C NMR analysis. The structure of two compounds was confirmed by single crystal X-ray diffraction. The photophysical properties of synthesized compounds were measured in a variety of organic solvents. The effects of substituents and solvents on UV-vis spectra and fluorescence emission were analyzed. All compounds were showed negative solvatochromism. The fluorescence emission of these derivatives was sensitive to solvent basicity and the large Stokes shifts (up to 129 nm, 4599 (cm-1)) were observed. The similar multicomponent reaction between naphthoquinone, bindone and pyridine derivatives provide the formation of stable non-fluorescent compound possessing zwitter-ionic structure.

Multicomponent Strategy to Pyrazolo[3,4-e]indolizine Derivatives under Microwave Irradiation

A simple and efficient one-pot construction of pyrazolo[3,4-e]indolizine derivatives via a diethylamine-catalyzed three-component domino reaction of arylglyoxals, cyclic 1,3-diones, and 5-aminopyrazoles under microwave irradiation is described. In this one-pot transformation, seven bonds and two new rings are efficiently formed. This synthesis was confirmed to follow the group-assisted-purification (GAP) chemistry process, which can avoid traditional recrystallization or chromatography purification methods.