The 50 most-cited articles in The Journal of Organic Chemistry, 2017

Mechanochemical activation achieved by grinding, shearing, pulling, or milling opens unique opportunities in synthetic organic chemistry. Common features are that mechanochemistry facilitates reactions with insoluble reactants, enables high-yielding solvent-free synthetic procedures, and shortens reaction times, among others. However, mechanochemical techniques can also alter chemical reactivity and selectivity compared to the analogous solution-based protocols. As a consequence, solvent-free milling can lead to different product compositions or equilibration mixtures than in solution. Reactions by milling have also allowed the trapping and characterization of elusive intermediates and materials. In this Perspective we highlight a few selected examples that illustrate the value of mechanochemistry in uncovering interesting chemical reactivity, which is often masked in typical liquid-phase synthesis.

Carbon monoxide is an important one-carbon source and can be incorporated in complex molecules via various transition-metal-catalyzed carbonylation reactions. In particular, palladium-catalyzed carbonylation reactions have found broad application in total synthesis of natural products. Examples are presented in this Synopsis to highlight recent progress in this area, including our own work in macrolide and spirocyclic molecule synthesis. In these selected cases, carbon monoxide functions as a one-carbon linchpin to facilitate building structural complexity and improving synthetic efficiency.

Abstract A one-pot Pd-catalyzed conversion of aryl iodide to aryl sulfonyl fluorides using DABSO and Selectfluor has been developed generating aryl sulfonyl fluorides in good to excellent yields. The reaction results in the generation of electronically and sterically diverse sulfonyl fluorides. Additionally, sulfonyl fluorides can be converted to aryl sulfonamides and sulfonic esters using Cs2CO3 under mild conditions.

Indolylmethanols have emerged as versatile reactants in catalytic asymmetric reactions because of the facile generation of reactive intermediates from these compounds. The most common indolylmethanols are 3-indolylmethanols and 2-indolylmethanols, and the reaction types applicable to these heterocycles mainly include catalytic enantioselective substitutions and cyclizations. Using indolylmethanols as reactants in catalytic asymmetric reactions enables the enantioselective construction of a variety of indole-containing frameworks.

Regioselective halogenation of arenes and heterocycles with N-halosuccinimides in fluorinated alcohols is disclosed. Under mild condition reactions, a wide diversity of halogenated arenes are obtained in good yields with high regioselectivity. Additionally, the versatility of the method is demonstrated by the development of one-pot sequential halogenation and halogenation-Suzuki cross-coupling reactions.

Abstract Iteratively executed with exquisite spatial and temporal control, the selective isomerization of polarized alkenes underpins a plethora of complex biological processes ranging from natural product biosynthesis through to the mammalian visual cycle. However, nature’s proficiency conceals the inherent difficulties in replicating this contra-thermodynamic transformation in the laboratory. Recently, we disclosed the first highly Z-selective isomerization of polarized alkenes, employing the cinnamoyl chromophore as a retinal surrogate under UV-irradiation (402 nm) with (−)-riboflavin (vitamin B2) as an inexpensive, organic photocatalyst (J. Am. Chem. Soc. 2015, 137, 11254–11257). This study was inspired by the propensity of crystalline (−)-riboflavin in the eyes of vertebrates to invert the intrinsic directionality of retinal isomerization. Herein, we extend this methodology to include a bioinspired, catalytic E → Z isomerization of α,β-unsaturated nitriles, thereby mimicking the intermediate Opsin-derived, protonated Schiff base in the visual cycle with simple polarized…

Recent advances in our understanding of lipid peroxidation, a degenerative process that is believed to play a key role in the pathogenesis of many diseases, are highlighted. In particular, the factors that control the kinetics and regio-/stereochemical outcomes of the autoxidation of both polyunsaturated fatty acids and sterols and the subsequent decomposition of the hydroperoxide products to cytotoxic derivatives are discussed. These advances promise to help clarify the role of lipid peroxidation in cell death and human disease.

In this paper, we report a general, efficient, and environmentally benign method for the one-pot cascade synthesis of quinazolin-4(3H)-ones via acceptorless dehydrogenative coupling of o-aminobenzamide with alcohols catalyzed by a simple Ni(II) catalyst, [Ni(MeTAA)], featuring a tetraaza macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)). A wide variety of substituted quinazolin-4(3H)-ones were synthesized in high yields starting from readily available benzyl alcohols and o-aminobenzamides. Several controlled reactions along with deuterium labeling studies were carried out to establish the acceptorless dehydrogenative nature of the reactions.

C-H) and amines (N-H) in the presence of catalytic iodine is reported. The reaction yields 3-aminoquinoxalinones in moderate to high yields under ambient conditions in dioxane as solvent and aqueous tert-butyl hydroperoxide (TBHP) as the terminal oxidant. The reaction is highly versatile and exhibits good functional group tolerance with a range of primary and secondary amines. It provides a practical access to pharmaceutically active 3-aminoquinoxalinone derivatives. Preliminary mechanistic studies reveal in situ iodination of the amine as the putative mode of activation.

Molecular iodine, an easy to handle solid, has been successfully employed as a catalyst in different organic transformations for more than 100 years. Despite being active even in very small amounts, the origin of this remarkable catalytic effect is still unknown. Both a halogen bond mechanism as well as hidden Brønsted acid catalysis are frequently discussed as possible explanations. Our kinetic analyses reveal a reaction order of 1 in iodine, indicating that higher iodine species are not involved in the rate-limiting transition state. Our experimental investigations rule out hidden Brønsted acid catalysis by partial decomposition of I 2 to HI and suggest a halogen bond activation instead. Finally, molecular iodine turned out to be a similar if not superior catalyst for Michael additions compared with typical Lewis acids.

Among organic azides, vinyl azides have shown versatile chemical reactivities in the recent development of new synthetic methodologies mainly for nitrogen-containing molecules. This synopsis highlights and discusses recent advances on use of vinyl azides in chemical synthesis as a radical acceptor and an enamine-type nucleophile.

The case is made for transitioning organic chemistry from a developed discipline that remains highly dependent upon organic solvents to one that will be sustainable, based on water as the reaction medium. Processes in hand that today achieve the same bond constructions characteristic of traditional organic synthesis, but can be accomplished under environmentally responsible conditions, are discussed as representative of the potential that lies ahead.

Halogenated natural products constitute diverse and promising feedstock for molecular pharmaceuticals. However, their solution-structure elucidation by NMR presents several challenges, including the lack of fast methods to compute 13 C chemical shifts for carbons bearing heavy atoms. We show that parametric corrections to DFT-computed chemical shifts in conjunction with rff -computed spin–spin coupling constants allow for fast and reliable screening of a large number of reported halogenated natural products, resulting in expedient structure validation or revision. In this paper, we examine more than 100 structures of halogenated terpenoids and other natural products with the new parametric approach and demonstrate that the accuracy of the combined method is sufficient to identify misassignments and suggest revisions in most cases (16 structures are revised). As the 1D 1 H and 13 C NMR data are ubiquitous and most routinely used in solution structure elucidation, this fast and efficient two-criterion method (nuclear spin–spin coupling and 13 C chemical shifts) which we term DU8+ is…

Novel iodine-induced sulfonylation and sulfenylation of imidazopyridines have been described using sodium sulfinates as the sulfur source. This strategy enables highly selective difunctionalization of imidazo[1,2-a]pyridine to access sulfones and sulfides in good yields. A wide range of substrates and functional groups were well-tolerated under optimized conditions. Moreover, control experiments have been conducted, indicating a radical pathway involved in the reaction mechanisms.

Among the palette of previously described fluorescent organic molecules, coumarins are ideal candidates for developing cellular and molecular imaging tools due to their high cell permeability and minimal perturbation of living systems. However, blue-to-cyan fluorescence emission is usually difficult in in vivo applications due to the inherent toxicity and poor tissue penetration of short visible light wavelengths. Here, we introduce a new family of coumarin-based fluorophores, nicknamed COUPY, with promising photophysical properties, including emission in the far-red/near-infrared (NIR) region, large Stokes shifts, high photostability, and excellent brightness. COUPY fluorophores were efficiently synthesized in only three linear synthetic steps from commercially available precursors, with the N-alkylation of a pyridine moiety being the key step at the end of the synthetic route, as it allows for the tuning of the photophysical properties of the resulting dye. Owing to their low molecular weights, COUPY dyes show excellent cell permeability and accumulate selectively in nucleoli…

A chiral phosphoric acid-catalyzed approach constructing dihydrocoumarin motifs by the addition of azlactones to para-quinone methides (p-QMs) was developed. The reaction proceeded smoothly with a wide range of p-QMs and azlactones to generate corresponding products in high yields with excellent diastereoselectivities (>19:1 dr) and enantioselectivities (up to 99% ee). Two possible pathways were proposed to explain the stereoselectivity.

Despite their importance, the synthesis of alkylated heterocycles from the cross-coupling of Lewis basic nitrogen heteroaryl halides with alkyl halides remains a challenge. We report here a general solution to this challenge enabled by a new collection of ligands based around 2-pyridyl-N-cyanocarboxamidine and 2-pyridylcarboxamidine cores. Both primary and secondary alkyl halides can be coupled with 2-, 3-, and 4-pyridyl halides as well as other more complex heterocycles in generally good yields (41 examples, 69% ave yield).

Herein, we describe an approach to quantifying and comparing functional group (FG) tolerance of synthetic reactions. Additive-based reaction screening is utilized as a tool for the objective comparison of reaction conditions as demonstrated in four case studies. This contributes to an understanding of factors limiting a reaction's FG tolerance and the identification of truly mild reactions.

Abstract Natural pigment chlorophyll was used as a green photosensitizer for the first time in a visible-light photoredox catalysis for the efficient synthesis of tetrahydroquinolines from N,N-dimethylanilines and maleimides in an air atmosphere. The reaction involves direct cyclization via an sp3 C–H bond functionalization process to afford products in moderate to high yields (61–98%) from a wide range of substrates with a low loading of chlorophyll under mild conditions. This work demonstrates the potential benefits of chlorophyll as photosensitizer in visible light catalysis.

A copper-catalyzed aerobic oxidative reaction between aromatics or heteroaromatics with KSCN is developed by using O 2 as the oxidant. The combination of Cu(OTf) 2, N, N, N ′, N ′-tetramethylethylenediamine (TMEDA) and BF 3 ·Et 2 O provides an efficient catalytic system, affording substituted thiocyanation products and 2-aminobenzothiazoles in excellent yields. The reaction also possesses a good functional group tolerance for both strong electron-withdrawing and electron-donating groups.

Pd-PEPPSI-IPr serves as a highly reactive precatalyst in the direct Suzuki-Miyaura cross-coupling of amides. An array of amides can be cross-coupled with a range of arylboronic acids in very good yields using a single, operationally simple protocol. The studies described represent the first use of versatile PEPPSI type of Pd-NHC complexes as catalysts for the cross-coupling of amides by N-C bond activation. The method is user-friendly, since it employs a commercially available, air- and moisture-stable Pd-PEPPSI-IPr complex. Pd-PEPPSI-IPr provides a significant improvement over all current Pd/phosphane catalysts for amide N-C bond activation. Mechanistic studies provide insight into the reaction rates of Pd-NHC-catalyzed cross-coupling of different amides, with Pd-PEPPSI-IPr being particularly effective for the cross-coupling of N-Boc carbamates under the developed conditions.

An efficient, green, and novel method for the synthesis of N-heterocycle-fused quinoxalines is reported herein. Dimethyl sulfoxide was used as both a reactant and a solvent in this reaction. A wide range of products in moderate to excellent yields were obtained, including pyrrolo[1,2-a]quinoxalines, indolo[1,2-a]quinoxalines, 1H-pyrrolo[3,2-c]quinolines, and benzo[4,5]imidazo[1,2-c]quinazolines.

Abstract While the use of triphenylphosphine as a reductant is common in organic synthesis, the resulting triphenylphosphine oxide (TPPO) waste can be difficult to separate from the reaction product. While a number of strategies to precipitate TPPO are available, none have been reported to work in more polar solvents. We report here that mixing ZnCl2 with TPPO precipitates a TPPO–Zn complex in high yield in several common polar organic solvents. The solvent compatibility of this procedure and the reliability of the precipitation in the presence of polar functional groups were examined to show the utility and limitations of this method.

A synthetic procedure to access 2-unsubstituted pyrrolidines and piperidines is presented. In the presence of MgI 2 as Lewis acid, donor–acceptor cyclopropanes or corresponding cyclobutanes were treated with 1,3,5-triazinanes, leading to the five- or six-membered ring systems under mild conditions in yields up to 93%. This protocol tolerates a great variety of functional groups and thus provides an efficient entry to this class of pyrrolidines and piperidines.

A substrate-controlled regioselective arylation of 2-indolylmethanols with indoles has been established, which efficiently afforded bis(indolyl)methane and 3,3'-bisindole derivatives in high yields and with a broad substrate scope (up to 98% yield, 36 examples). This approach will not only provide an important strategy for the diversified synthesis of bis(indolyl)methane and 3,3'-bisindole derivatives but also serve as a good example for substrate-controlled regioselective reactions.

Here, we describe a photoredox-assisted catalytic system for the direct reductive coupling of two carbon electrophiles. Recent advances have shown that nickel catalysts are active toward the coupling of sp 3 -carbon electrophiles and that well-controlled, light-driven coupling systems are possible. Our system, composed of a nickel catalyst, an iridium photosensitizer, and an amine electron donor, is capable of coupling halocarbons with high yields. Spectroscopic studies support a mechanism where under visible light irradiation the Ir photosensitizer in conjunction with triethanolamine are capable of reducing a nickel catalyst and activating the catalyst toward cross-coupling of carbon electrophiles. The synthetic methodology developed here operates at low 1 mol % catalyst and photosensitizer loadings. The catalytic system also operates without reaction additives such as inorganic salts or bases. A general and effective sp 2 –sp 3 cross-coupling scheme has been achieved that exhibits tolerance to a wide array of functional groups.

A stereoselective synthesis of (E)-vinyl sulfones has been developed via electrochemical oxidative N-S bond cleavage of aromatic sulfonylhydrazides, followed by cross-coupling reactions with cinnamic acids to form the C-S bond. The protocol proceeded smoothly to afford (E)-vinyl sulfones in good yields with wide substrate scope under metal-free and halogen-free conditions.

We report an operationally convenient room temperature hydroboration of aldehydes and ketones employing Fe(acac) 3 as precatalyst. The hydroboration of aldehydes and ketones proceeded efficiently at room temperature to yield, after work up, 1° and 2° alcohols; chemoselective hydroboration of aldehydes over ketones is attained under these conditions. We propose a σ-bond metathesis mechanism in which an Fe–H intermediate is postulated to be a key reactive species.

The copper-catalyzed cyclization of activated alkenes with cyclobutanone O-acyl oximes under redox-neutral conditions has been reported. This facile protocol provided an efficient approach to a variety of cyanoalkylated oxindoles and dihydroquinolin-2(1H)-ones with a broad substrate scope and excellent functional group tolerance. In this reaction, sequential C-C bond cleavage, radical addition, and cyclization processes were involved, wherein multiple bonds were constructed in a one-pot reaction. Mechanistic studies suggest that the reaction probably proceeded via a radical pathway.

Electrochemical studies of the reduction and oxidation reactions of five different organic nitroxyls have been performed across a wide pH range (0–13). The resulting Pourbaix diagrams illustrate structural effects on their various redox potentials and on the p K a values of the corresponding hydroxylamine and hydroxylammonium ions. Evidence is also given for the reversible formation of a hydroxylamine N -oxide when nitroxyls are oxidized in alkaline media. Structural effects on the thermodynamics of this reaction are assessed.

The palladium-catalyzed ortho-selective chlorination of N-quinolinylbenzamide derivatives with hydrochloric acid was achieved under anodic oxidation conditions. The use of 5,7-dichloro-8-quinolinyl group as directing group was effective for the selective chlorination, and the reaction was applicable to benzamide derivatives bearing various functional groups. Synthesis of vismodegib was also completed using the palladium-catalyzed electrochemical C-H chlorination in two different steps.

An efficient, direct C6-arylation of 2-pyridones has been successfully accomplished with quinone diazides under Rh(III)-catalyzed redox-neutral conditions. The optimized method is simple, mild, and highly regioselective with a broad substrate scope. The strict regioselectivity is guided by the pyridyl substituent attached to the nitrogen of the pyridone ring. As the directing 2-pyridyl group can easily be removed at any suitable stage after functionalization, the method provides a facile access to complex heteroarylated phenol moieties by wide-ranging heterocyclic scaffolds.

Radical alkylation of imines with 4-alkyl-1,4-dihydropyridines cocatalyzed by iridium/ruthenium complex and Brønsted acid under visible light irradiation has been achieved. Both aldimines and ketimines can undergo this transformation. Common functional groups, such as hydroxyl groups, ester, amide, ether, cyanide, and heterocycles, can be tolerated in this reaction. A variety of structurally diverse amines (57 examples) have been produced with up to 98% isolated yields using this method.

Esters are valuable electrophiles for cross-coupling due to their ubiquity and ease of synthesis. However, harsh conditions are traditionally required for the effective cross-coupling of ester substrates. Utilizing a recently discovered precatalyst, Pd-catalyzed Suzuki-Miyaura and Buchwald-Hartwig reactions involving cleavage of the C(acyl)-O bond of aryl esters that proceed under mild conditions are reported. The Pd(II) precatalyst is highly active because it is reduced to the Pd(0) active species more rapidly than previous precatalysts.

The synthesis of a series of push-pull derivatives bearing triphenylamine electron-donating group, cyclopenta[c]thiophen-4,6-dione electron acceptor and various π-linkers including (hetero)aromatic fragments is reported. All target chromophores with systematically varied π-linker structure were further investigated by electrochemistry, absorption measurements, and EFISH experiments in conjunction with DFT calculations. Based on electrochemical and photophysical measurements, when a polarizable 2,5-thienylene moiety is embedded into the chromophore π-backbone the highest intramolecular charge transfer (ICT) is observed. Benzene, pyrimidine, and pyridazine derivatives exhibit lower polarizability and extent of the ICT across these π-linkers. The elongation of the π-conjugated system via additional ethenylene linker results in a significant reduction of the HOMO-LUMO gap and an enhancement of the NLO response. Whereas it does not significantly influence electrochemical and linear optical properties, the orientation of the pyrimidine ring seems to be a key parameter on the μβ value due…

A relatively green oxidative C═C bond cleavage of alkenes was achieved by organoselenium-catalyzed alkene oxidation reaction in ethanol with hydrogen peroxide, affording carbonyl compounds under relatively mild conditions. It is a new reaction style for the organoselenium-catalyzed oxidation of alkenes and largely contributes to the growing field of organoselenium catalysis.

2′-Aminoacetophenones undergo a C(sp 3 )–H oxidation followed by intramolecular C–N bond formation by virtue of a simple electrochemical oxidation in the presence of n -Bu 4 NI, providing various isatins with moderate to good yields. The reaction intermediates were detected, and a radical-based pathway was proposed.

-mediated direct oxidative coupling of aromatic alkenes with thiols toward vinyl sulfones has been developed under metal-free conditions. This methodology provides a convenient and efficient approach to various (E)-vinyl sulfones from readily available starting materials with excellent regioselectivity. The present oxidative coupling reaction, not only expands the scope of functionalization of alkenes with thiols, but also makes it a practical and powerful complement to traditional methods for the synthesis of (E)-vinyl sulfones.

Transition-metal-catalyzed activation of amide N–C(O) bonds proceeds via selective metal insertion into the carbon–nitrogen amide bond. Herein, we demonstrate that N -acylanilines (anilides), the first class of planar amides that have been shown to undergo selective amide N–C cross-coupling reactions, feature a significantly decreased barrier to rotation around the amide N–C(O) bond. Most significantly, we demonstrate that amide n N → π* C═O resonance in simple anilides can be varied by as much as 10 kcal/mol. The data have important implications for the design of N–C(O) amide cross-coupling reactions and control of the molecular conformation of anilides by resonance effects.

The Mn(OAc) 3 -promoted oxidative phosphonylation of N, N -dimethylenaminones with H-phosphonates, involving a chemo- and regioselective C sp 2 –C sp 2 bond cleavage and C sp 3 –P bond formation in one step, provided successfully functionalized β-ketophosphonates under mild reaction conditions. Oxidative C sp 3 –H/P–H cross-coupling reactions via C sp 3 –C(C═O) bond cleavage and mechanistic studies are conducted preliminarily, and a possible mechanism is proposed. This novel method proceeds in good to excellent yields, shows operational simplicity, broad substrate scope, and large-scale preparation.

The indirect ("ex-cell") electrochemical synthesis of benzoxazoles from imines using a redox mediator based on the iodine(I)/iodine(III) redox couple is reported. Tethering the redox-active iodophenyl subunit to a tetra-alkylammonium moiety allowed for anodic oxidation to be performed without supporting electrolyte. The mediator salt can be easily recovered and reused. Our "ex-cell" approach toward the electrosynthesis of benzoxazoles is compatible with a range of redox-sensitive functional groups. An unprecedented concerted reductive elimination mechanism for benzoxazole formation is proposed on the basis of control experiments and DFT calculations.

Photoredox-catalyzed hydrodifluoroalkylation of alkenes proceeded smoothly in the presence of a Hantzsch ester as a hydrogen source under visible light irradiation. The reaction was also applicable to the hydrodifluoroalkylation of alkynes, and a continuous photo flow reaction was also successful.

Polysubstituted allyl groups, for example, the prenyl group, are valuable synthetic handles and widely encountered in bioactive compounds. Reported herein is a manganese(I)-catalyzed direct C-H coupling with allenes for the efficient assembly of allylated arenes. The protocol offers an extremely high level of atom-economy and is particularly suited for the introduction of 1,1-disubstitiuted allyl groups, as exemplified by the quantitative syntheses of a variety of prenylated indoles. The practicality of this method was evidenced by a gram-scale synthesis with a lower catalyst loading of manganese(I) (2.5 mol %, 95% yield). Experimental mechanistic studies were conducted, and a possible reaction mechanism was proposed.

An efficient copper-catalyzed carbenoid insertion reaction of α-diazo carbonyl compounds into Si-H and S-H bonds was developed. A wide range of α-silylesters and α-thioesters was obtained in high yields (up to 98%) from α-diazoesters using 5 mol% of a simple copper(I) salt as catalyst. Using 0.05 mol% of the same catalyst, α-diazoketones led to α-silylketones in low to good yields (up to 70%).

Simple and high-yielding strategies for the production of a variety of sulfones and sulfonamides, using thiosulfonates synthesized by copper-catalyzed aerobic dimerization, are reported. Although thiosulfonates are an old class of compound, practical methods for their synthesis and utilization have not been rigorously developed. In this study, we revisit the reactions of easily accessible thiosulfonates to form sulfinate anions. Because of the similar reactivity of thiosulfonates and metal sulfinates derived from toxic SO 2, thiosulfinates are proposed to be stable, nontoxic alternatives to metal sulfinate salts.

The visible light-mediated C-3 alkoxylation of imidazopyridines with alcohols has been achieved using rose bengal as an organic photoredox catalyst at room temperature. Widely abundant air acts as the terminal oxidant that avoids the use of a stoichiometric amount of peroxo compounds. A wide range of functional groups could be tolerated under the reaction conditions to produce C(sp 2 )–H alkoxylated products in high yields.

Compounds that can be labeled as “aromatic chameleons” are π-conjugated compounds that are able to adjust their π-electron distributions so as to comply with the different rules of aromaticity in different electronic states. We used quantum chemical calculations to explore how the fusion of benzene rings onto aromatic chameleonic units represented by biphenylene, dibenzocyclooctatetraene, and dibenzo[ a, e ]pentalene modifies the first triplet excited states (T 1 ) of the compounds. Decreases in T 1 energies are observed when going from isomers with linear connectivity of the fused benzene rings to those with cis- or trans-bent connectivities. The T 1 energies decreased down to those of the parent (isolated) 4 n π-electron units. Simultaneously, we observe an increased influence of triplet state aromaticity of the central 4 n ring as given by Baird’s rule and evidenced by geometric, magnetic, and electron density based aromaticity indices (HOMA, NICS- XY, ACID, and FLU). Because of an influence of triplet state aromaticity in the central 4 n π-electron units, the most stabilized…

Asymmetric arylation of secondary silanes catalyzed by a Pd-chiral phosphoramidite complex was developed for application to low-molecular-weight circularly polarized luminescence (CPL) materials. The asymmetric arylation provided a convenient, efficient synthetic method for a variety of chiral tertiary silanes ( 2 – 21 ), which were key intermediates for preparing the quaternary silicon center. A stepwise, one-pot procedure was used to transform the appropriate aryl iodide to the quaternary silane ( 22 ) with good yield and enantioselectivity. Among compounds synthesized in this work, four optically pure tertiary silanes ( 18 – 21 ) were selected to investigate the relationship between the structure and optical properties. Optically pure ( S,S )- 21 displayed the highest CPL emission with a high fluorescence quantum yield ( g lum: +0.008, Φ F: 0.42). This simple molecular design provides new strategies for developing small organic CPL dyes.

3-Cyanomethylated imidazopyridines were synthesized via a visible light-promoted reaction of imidazopyridines with bromoacetonitrile or iodoacetonitrile catalyzed by fac -Ir(ppy) 3 under mild conditions. For the substrates with various substituents on benzene or pyridine ring, the reaction proceeded smoothly to give the corresponding products in moderate to good yields. The synthetic utility of this visible-light-induced reaction has been illustrated in the efficient synthesis of zolpidem and alpidem.

(Diacetoxy)iodobenzene (PIDA)-mediated direct oxidative C-H amination for the synthesis of 3-amino substituted imidazopyridines has been achieved under metal-free conditions at room temperature in short reaction times. This methodology is also applicable for the regioselective amination of indolizines. Experimental results suggest that the reaction likely proceeds through a radical pathway.