Palladium-Catalyzed Tandem Cyclization of Bromoenynes through Aromatic CH Bond Functionalization

Palladium-Catalyzed Synthesis of Fluorescent Benzo[4,5]imidazo[1,2-a]pyridines through Annulation Reaction of Benzimidazoles and Alkynyl Bromides with Internal Alkynes

An efficient synthesis of fused azapolycycles based on (benz)imidazole and pyridine scaffolds has been developed. In all cases, the first nucleophilic addition of (benz)imidazoles to alkynyl bromides in tert-pentyl alcohol can proceed in a stereoselective manner to provide (Z)-N-(1-bromo-1-alken-2-yl)benzimidazoles at 110 °C. Sequentially, these adducts containing alkenyl bromide can undergo Pd-catalyzed intermolecular C-H annulation in the presence of internal alkynes in dimethylacetamide, affording fluorescent (benz)imidazole-fused pyridines in good to high yields. These compounds generally exhibit blue or green fluorescences (454-503 nm for solution states and 472-506 nm for solid states), and the fluorescence quantum yields remained in 0.19-0.89 and 0.02-0.74 for solution and solid states, respectively.

Palladium-catalyzed sp(3) CH activation of simple alkyl groups: direct preparation of indoline derivatives from N-alkyl-2-bromoanilines

The sp3 C-H activation of a simple alkyl group catalyzed by palladium(0) provides a novel and convenient strategy for the synthesis of various indolines from simple precursors, such as N-alkyl-2-bromoanilines. This study demonstrates that assisting moieties in the substrate such as a pyridine or quaternary carbon are not always necessary for sp3 C-H activation.

Two palladium-catalyzed domino reactions from one set of substrates/reagents: efficient synthesis of substituted indenes and cis-stilbenoid hydrocarbons from the same internal alkynes and hindered Grignard reagents

Two types of domino reactions from the same internal alkynes and hindered Grignard reagents based on carbopalladation, Pd-catalyzed cross-coupling reaction, and a C-H activation strategy are described. The realization of these domino reactions relied on the control of the use of the ligand and the reaction temperature. Our study provides efficient access to useful polysubstituted indenes and cis-substituted stilbenes and may offer a new means of development of tandem/domino reactions in a more efficient way. [reaction: see text].

Sequence-Specific Detection of Femtomolar DNA via a Chronocoulometric DNA Sensor (CDS): Effects of Nanoparticle-Mediated Amplification and Nanoscale Control of DNA Assembly at Electrodes

We herein report a novel nanoparticle-based electrochemical DNA detection approach. This DNA sensor is based on a "sandwich" detection strategy, which involves capture probe DNA immobilized on gold electrodes and reporter probe DNA labeled with gold nanoparticles that flank the target DNA sequence. Electrochemical signals are generated by chronocoulometric interrogation of [Ru(NH(3))(6)](3+) that quantitatively binds to surface-confined capture probe DNA via electrostatic interactions. We demonstrated that the incorporation of a gold nanoparticle in this sensor design significantly enhanced the sensitivity and the selectivity. Nanoscale control of the self-assembly process of DNA probes at gold electrodes further increased the sensor performance. As a result of these two combined effects, this DNA sensor could detect as low as femtomolar (zeptomoles) DNA targets and exhibited excellent selectivity against even a single-base mismatch. In addition, this novel DNA sensor showed fairly good reproducibility, stability, and reusability.

Understanding Sulfone Behavior in Palladium-Catalyzed Domino Reactions with Aryl Iodides

Unlike traditionally used acyclic 1,2-disubstituted alkenes, the reaction of alpha,beta-unsaturated phenyl sulfones with aryl iodides under Heck reaction conditions takes place mainly by means of a four-component domino process, involving one unit of the alkene and three units of the aryl iodide, affording substituted 9-phenylsulfonyl-9,10-dihydrophenanthrenes. We report here the results of a computational study on the mechanism of this domino arylation reaction. Based on these results we can explain why vinyl sulfones, unlike other electron-deficient alkenes such as enones, preferentially follow this domino pathway instead of the usual Heck pathway. The key step is a C-H activation process in which a five-membered palladacycle is formed. The greater ability of vinyl sulfones, relative to enones, to reach the transition state that leads to the formation of the initial palladacycle makes the difference.

Development of Useful Reactions Based on the Novel Reactivities of Allenic Compounds and Their Application to Tandem Cyclizations

This review highlights a recent study on allenic compounds by the author's group. In the first section, the organocopper-mediated ring-opening reaction of ethynylaziridines and palladium-catalyzed reductive synthesis of allenes are described. In the second section, palladium-catalyzed stereoselective cyclization of allenes, including the tandem reaction, leading to aziridines, pyrrolidines, benzoisoindoles, and cyclopropanes is presented. The final section reviews aziridination and medium-ring formation due to the intramolecular reaction of bromoallenes. The latter reaction is based on the author's recent discovery that bromoallenes can act as allylic dication equivalents in the presence of a palladium catalyst and alcohol.