Keiichi Hirano 교수

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.

Abstract N-Heterocyclic carbene (NHC)-catalyzed transformations have found increasing interest in the last years. Recently, dual catalytic approaches using NHCs in combination with a second catalyst such as another organocatalyst or a metal-based catalyst or by the NHC itself have emerged. The careful choice of the proper combination of catalysts allows two compatible yet independent catalytic systems in one-pot to undergo tandem processes. Moreover, simultaneous action of two activators in a bo

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 te

Abstract The N‐heterocyclic carbene‐catalyzed conjugate umpolung of differently substituted α,β‐unsaturated aldehydes is described. Coupling of these compounds with a variety of trifluoromethylated ketones results in the selective formation of fluorinated γ‐butyrolactones. Using thiazolium‐derived N‐heterocyclic carbenes, the unlike stereoisomers are formed predominantly, whereas the imidazol‐2‐ylidene IMes results in lower selectivities and the preferred formation of the like isomer.

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.

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 wi

A novel method for the preparation of diverse allylic boronates from simple allylic alcohols is reported.

A combination of dimethylzinc, perfluoroalkyl iodide, and LiCl afforded a new type of perfluoroalkyl (RF ) zinc ate complex. These complexes show much greater thermal stability than conventional perfluorinated metal species, such as RF -lithium species and Grignard reagents, and they can be used at room temperature or higher. The results of DFT calculations on the origin of the enhanced stability are reported and the synthetic utility of RF -zincate complexes is demonstrated.

An unprecedented boron-containing fluorophore, π-extended cis-stilbene, obtained via alkynylboration reaction of alkynamide is reported. Boron-containing π-extended cis-stilbenes emit fluorescence with high quantum yields in the solid state and exhibit aggregation-induced emission enhancement. The broad substrate scope of the alkynylboration reaction offers facile access to electronically diverse structures, enabling fine-tuning of light absorption/emission characteristics. The boron-containing

Abstract 1‐Boraphenalenes, a class of boron‐doped polyaromatic hydrocarbons, were synthesized by nucleophilic diboration reaction of alkynes. Activation of diboron reagents with a highly basic sp 2 ‐carbanion results in very fast successive C−B bond formations to construct the boracycle. This methodology is characterized by high chemoselectivity, affording a wide variety of 1‐boraphenarenes with diverse polar substituents. The endocyclic boron can be arylated conveniently in one pot, and the per

Carefully designed cyclic hydrosilanes enable <i>trans</i>-selective hydrosilylation of unactivated alkynes without transition metal catalysts via silicate formation. Employment of sterically demanding bidentate ligands of silicon increases steric congestion upon silicate formation, and this strain-imposing strategy facilitates hydride transfer. This hydrosilylation provides efficient access to diverse benzosiloles, silaphenalenes, and related silacycles.

Various carboxylic acids were directly transformed into the corresponding ketones by utilizing organozinc ate complexes, which provide high chemoselectivity without any overreaction to the undesired tertiary carbinol, owing to formation of a stable tetrahedral zincioketal intermediate. This method offers good overall atom/step/pot economy and operational simplicity.

Abstract Here, we review recent progress in transition‐metal‐free inter‐element boration reactions via Lewis‐basic activation of various boron reagents, focusing mainly on the boration reactions of carbon‐carbon multiple bonds without an electron‐withdrawing (activating) group and those with an electron‐withdrawing group where the polarity of the addition reaction is inverse to the “natural” reactivity. magnified image

The catalysis of two successive bromine–lithium exchange reactions, referred to as a “halogen dance”, by lithium aryltrifluoroborate is reported. At a loading of 10 mol %, this catalyst exhibited efficient activity for bromo group transfer and was applicable to various brominated pyridines. Density functional theory calculations were consistent with the proposed mechanism, where the catalyst provided a bromine atom to the mono- or dibrominated substrate and the resulting debrominated catalyst th