Alkene Isomerization–Hydroarylation Tandem Catalysis: Indole C2‐Alkylation with Aryl‐Substituted Alkenes Leading to 1,1‐Diarylalkanes

A cobalt‐N‐heterocyclic carbene catalyst generated from CoBr₂, imidazolium salt, and cyclohexylmagnesium bromide was found to promote the imine‐directed C2‐alkylation of indoles with nonconjugated arylalkenes through a tandem alkene isomerization–hydroarylation process, affording 1,1‐diarylalkanes with exclusive regioselectivity. The feasibility of the tandem catalysis was demonstrated for allyl‐, homoallyl‐, and bishomoallylbenzene derivatives. The catalytic system is also applicable to a variety of β‐substituted styrene derivatives. Mechanistic experiments using deuterium‐labeled indole substrate and Grignard reagent provided insight into the cobalt‐mediated C? H activation step, which likely involves exchange of the C2‐hydrogen atom of the former and the β‐hydrogen atoms of the latter.     

Synthesis of Novel Imidazole-4,5-Dicarboxamide Derivatives

Imidazolecarboxamide derivatives have been known to exhibit biological activity, especially antiparasitic activity.¹ To date imidazole-4(5)-monocarboxamide derivatives and symmetrical imidazole-4,5-dicarboxamide derivatives have been investigated.¹ However, unsymmetrical imidazole-4,5-dicarboxamide derivatives, having different carboxamide groups, have not been investigated. Therefore, the author was prompted to devise a synthetic method for unsymmetrical diamide derivatives.     

Iron-catalyzed direct arylation through directed C-H bond activation

An iron-catalyzed C-C bond formation reaction of a nitrogen-containing aromatic compound with an arylzinc reagent takes place at 0 degrees C in a good to quantitative yield. The reaction involves a C-H bond activation directed by a neighboring nitrogen atom. The important additives in this reaction are 1,10-phenanthroline, tetramethylethylenediamine, and 1,2-dichloro-2-methylpropane, in the absence of which a very low product yield was observed.     

Cobalt-catalyzed, room-temperature addition of aromatic imines to alkynes via directed C-H bond activation

A quaternary catalytic system consisting of a cobalt salt, a triarylphosphine ligand, a Grignard reagent, and pyridine has been developed for chelation-assisted C-H bond activation of an aromatic imine, followed by insertion of an unactivated internal alkyne that occurs at ambient temperature. The reaction not only tolerates potentially senstitive functional groups (e.g., Cl, Br, CN, and tertiary amide), but also displays a unique regioselectivity. Thus, the presence of substituents such as methoxy, halogen, and cyano groups at the meta-position of the imino group led to selective C-C bond formation at the more sterically hindered ortho positions. Under acidic conditions, the hydroarylation products of dialkyl- and alkylarylacetylenes underwent cyclization to afford benzofulvene derivatives, while those of diarylacetylenes afforded the corresponding ketones in moderate to good yields. A mechanistic investigation into the reaction with the aid of deuterium-labeling experiments and kinetic analysis has indicated that oxidative addition of the ortho C-H bond is the rate-limiting step of the reaction. The kinetic analysis has also shed light on the complexity of the quaternary catalytic system.     

Photomagnetism of a sym-cis-dithiocyanato iron(II) complex with a tetradentate N,N'-bis(2-pyridylmethyl)1,2-ethanediamine ligand

A comprehensive study of the magnetic and photomagnetic behaviors of cis-[Fe(picen)(NCS)(2) ] (picen = N,N'-bis(2-pyridylmethyl)1,2-ethanediamine) was carried out. The spin-equilibration was extremely slow in the vicinity of the thermal spin-transition. When the cooling speed was slower than 0.1?K min(-1), this complex was characterized by an abrupt thermal spin-transition at about 70?K. Measurement of the kinetics in the range 60-70?K was performed to approach the quasi-static hysteresis loop. At low temperatures, the metastable HS state was quenched by a rapid freezing process and the critical T(TIESST) temperature, which was associated with the thermally induced excited spin-state-trapping (TIESST) effect, was measured. At 10?K, this complex also exhibited the well-known light-induced excited spin-state-trapping (LIESST) effect and the T(LIESST) temperature was determined. The kinetics of the metastable HS states, which were generated from the freezing effect and from the light-induced excitation, was studied. Single-crystal X-ray diffraction as a function of speed-cooling and light conditions at 30?K revealed the mechanism of the spin-crossover in this complex as well as some direct relationships between its structural properties and its spin state. This spin-crossover (SCO) material represents a fascinating example in which the metastability of the HS state is in close vicinity to the thermal spin-transition region. Moreover, it is a beautiful example of a complex in which the metastable HS states can be generated, and then compared, either by the freezing effect or by the LIESST effect.     

Anomaly of CH4 molecular assembly confined in single-wall carbon nanohorn spaces

Vibrational-rotational properties of CH(4) adsorbed on the nanopores of single-wall carbon nanohorns (SWCNHs) at 105-140 K were investigated using IR spectroscopy. The difference vibrational-rotational bands of the ν(3) and ν(4) modes below 130 K show suppression of the P and R branches, while the Q branches remain. The widths of the Q branches are much narrower than in the bulk gas phase due to suppression of the Doppler effect. These results indicate that the rotation of CH(4) confined in the nanospaces of SWCNHs is highly restricted, resulting in a rigid assembly structure, which is an anomaly in contrast to that in the bulk liquid phase.     

Chaos via torus breakdown from a four-dimensional autonomous oscillator with two diodes

By using a remarkably simple and natural degenerate technique, the mechanism of chaos via torus breakdown observed in a simple four-dimensional autonomous circuit including two diodes is investigated rigorously. This degenerate technique is uniquely comparable to the well-known slow-fast singular perturbation method. The idealized case where the diodes are assumed to operate as switches is considered. In this case, the governing equation is represented by a constrained equation, and the Poincaré mapping is derived rigorously as the circle map. The torus breakdown in the four-dimensional autonomous circuit is well explained by the Poincaré mapping. The theoretical results are verified by laboratory experiment.     

Simultaneous measurement of surface shape and absolute optical thickness of a glass plate by wavelength tuning phase-shifting interferometry

The absolute optical thickness and the surface shape of a glass plate of 7-in. square and 3.1mm thick was simultaneously measured by three-surface interferometry using a wavelength tuning Fizeau interferometer. The wavelength of a tunable diode laser is scanned linearly from 632 to 642 nm, at which the initial and the final phases of the interference fringes for the surface shape and for the optical thickness were separated and measured by a tunable phase-shifting technique. The number of phase variations in the interference fringes during the scanning is counted by discrete Fourier analysis, in which systematic errors caused by a nonlinearity in the wavelength scanning is corrected by a correlation analysis between the observed and theoretical interference fringes. Experimental results demonstrate that the systematic errors in the measured value were 15 nm for the surface shape and 0.6 μm for the absolute optical thickness.