Keiichi Hirano

N-heterocyclic carbene-catalyzed hydroacylation of unactivated double bonds.

An intramolecular N-heterocyclic carbene (NHC)-catalyzed hydroacylation of unactivated double bonds is reported. Systematic variation of the catalyst structure revealed an N-mesitylthiazolylidene annulated with a seven-membered ring to be especially reactive. This NHC enables a unique C-C bond-forming reaction to afford substituted chroman-4-ones in moderate to excellent yields, even ones containing all-carbon quaternary centers.

Design, Generation, and Synthetic Application of Borylzincate: Borylation of Aryl Halides and Borylzincation of Benzynes/Terminal Alkyne

Borylzincate was generated in situ from dialkylzinc, diboron, and metal alkoxide. Model DFT calculations showed that although the formation of borylzincate is kinetically favorable, it is thermodynamically unfavorable. Therefore, we designed a successive reaction sequence that would provide a compensating energy gain. This enabled Zn-catalyzed borylation of aryl halides and borylzincation of benzynes and terminal alkyne from diborons without the need for any cocatalyst.

A Modular Synthesis of Highly Substituted Imidazolium Salts

A versatile and modular one-pot method for the preparation of differently substituted symmetrical and unsymmetrical imidazolium salts is reported, and 19 examples are given. In the key step, readily available formamidines and alpha-halo ketones are coupled to give imidazolinium salts 3, followed by imidazolium salt formation by acylation-induced elimination. For many substitution patterns of the imidazolium salt products, this efficient strategy compares favorably with well-known processes in terms of yield, ease of synthesis, and robustness.

Copper-Catalyzed Synthesis of 2-Unsubstituted, N-Substituted Benzimidazoles

An efficient copper-catalyzed intramolecular arylation of formamidines forming 2-unsubstituted benzimidazoles in excellent yields is reported. Sixteen examples bearing sterically demanding substituents on nitrogen like Mes, 2,6-diisopropylphenyl, or 2-tert-butylphenyl and tolerating various functional groups demonstrate the utility of this method.

Trans-Diborylation of Alkynes: Pseudo-Intramolecular Strategy Utilizing a Propargylic Alcohol Unit

We present the first trans-selective diborylation reaction of alkynes. By means of theoretical calculation-assisted reaction analysis, we designed a pseudo-intramolecular reaction of diboron, propargyl alcohol, and a base to facilitate B-B bond activation and C-B bond formation with high efficiency. This approach provides synthetically versatile and densely functionalized 4-borylated 1,2-oxaborol-2(5H)-oles (vinyldiboronates) in a straightforward manner. Detailed computational analysis showed that the directing alkoxide functionality markedly lowers the activation energy of B-C bond formation.

Perfect crystal X-ray phase retarders

Abstract X-ray phase retarders of perfect crystals are discussed on the basis of a dynamic theory of diffraction. Although all conceivable diffraction geometries can be used for a phase retarder, transmission of less absorptive crystals in both Laue and Bragg geometries as well as reflection and transmission of absorptive crystals in Laue geometry give practical solutions for circularly polarized X-ray generation with synchrotron radiation (SR). Some SR beamline optics using these phase retarders are presented.

Direct Hydroxylation and Amination of Arenes via Deprotonative Cupration

Deprotonative directed ortho cupration of aromatic/heteroaromatic C-H bond and subsequent oxidation with t-BuOOH furnished functionalized phenols in high yields with high regio- and chemoselectivity. DFT calculations revealed that this hydroxylation reaction proceeds via a copper (I → III → I) redox mechanism. Application of this reaction to aromatic C-H amination using BnONH2 efficiently afforded the corresponding primary anilines. These reactions show broad scope and good functional group compatibility. Catalytic versions of these transformations are also demonstrated.

Dialkylzinc-mediated cross-coupling reactions of perfluoroalkyl and perfluoroaryl halides with aryl halides.

A highly chemoselective perfluoroalkylation reaction of aromatic halides is reported. Thermally stable perfluoroalkylzinc reagents, generated by a rapid halogen-zinc exchange reaction between diorganozinc and perfluoroalkyl halide species, couple with a wide range of aryl halides in the presence of a copper catalyst, in moderate to high yields. Good stability of the perfluoroalkylzinc species was indicated by DFT calculation and the reagents were storable for at least three months under argon without loss of activity. This method is applicable to gram-scale synthesis, and its functional group tolerance compares favorably with reported protocols.

A multiple crystal diffractometer for generation and characterization of circularly polarized x rays at the Photon Factory (invited)

A multiple crystal diffractometer for polarization optical experiments in x‐ray region was constructed at the Photon Factory. Using an x‐ray phase retarder of transmission type in Bragg geometry, tunable‐wavelength circular polarized x rays of both helicities were produced with high degree of circular polarization. A method of complete determination of the polarization states in x‐ray region was developed with the reverse use of the phase retarder. Polarization switching with a frequency of 0.3 Hz was performed by flipping the phase retarder in a bistable mode. An optical scheme of producing highly intense circular polarizations using the phase retarder and an x‐ray undulator is discussed.

Amidocuprates for Directed ortho Cupration: Structural Study, Mechanistic Investigation, and Chemical Requirements†

Organocuprate(I) complexes are immensely valuable reagents for both industrial and research chemistry. During the past few decades, heteroleptic organocuprates bearing alkynyl, cyano, phenylthio, and phosphino groups have secured an important place in organic synthesis. Organo-amidocuprates also represent an important class of heteroleptic cuprates in organic transformations, especially in stereoselective syntheses. In this context, we have recently proposed new uses for amidocuprates, TMPCu-ates ([RCu(TMP)(CN)Li]; R = alkyl, phenyl, and TMP; TMP = 2,2,6,6-tetramethylpiperidido), which promote the highly chemoselective, directed ortho cupration of multifunctionalized aromatic compounds under mild conditions. The aryl cuprate intermediate can be employed not only in the trapping of electrophlies, but also in oxidative ligand coupling to form new C C bonds with alkyl/aryl groups or to introduce a hydroxy group (Scheme 1). Organocuprate(I) chemistry is dominated by two structure types: the Gilman-type and the Lipshutz-type. The basic diorganocuprate(I) unit in each adopts a linear [R-CuR] arrangement. Gilman-type species are known to exhibit homodimeric structures (Scheme 2a). Theoretical predictions of a preference for head-to-tail dimerization of heteroleptic cuprates have been confirmed by the structure of [MesCu(NBn2)Li] (Mes = mesityl, Bn = benzyl), [9]