Hikaru Yanai

Highly effective vinylogous Mukaiyama-Michael reaction catalyzed by silyl methide species generated from 1,1,3,3-tetrakis(trifluoromethanesulfonyl)propane.

Silyl methide species in situ generated from 1,1,3,3-tetrakis(trifluoromethanesulfonyl)propane (Tf(2)CHCH(2)CHTf(2)) performed as an excellent acid catalyst for the vinylogous Mukaiyama-Michael reaction of alpha,beta-unsaturated ketones with 2-silyloxyfurans. Notably, the required loading of Tf(2)CHCH(2)CHTf(2) to obtain the 1,4-adducts in reasonable yield was significantly low (from 0.05 to 1.0 mol %). This carbon acid-mediated VMM reaction provides a powerful synthetic methodology to construct highly substituted gamma-butenolide structure.

Tetrakis(trifluoromethanesulfonyl)propane: highly effective Brønsted acid catalyst for vinylogous Mukaiyama–Michael reaction of α,β-enones with silyloxyfurans

1,1,3,3-Tetrakis(trifluoromethanesulfonyl)propane was found as an excellent Brønsted acid catalyst for the Mukaiyama-Michael reaction of alpha,beta-enones with 2-silyloxyfurans; using beta,beta-disubstituted enones as a Michael acceptor, an excellent yield construction of quaternary carbon centers could be achieved; in addition, very low catalyst loading of Brønsted acid was used in a range from 0.05 to 1.0 mol%.

Carbon acid induced Mukaiyama aldol type reaction of sterically hindered ketones.

1,1,3,3-Tetrakis(trifluoromethanesulfonyl)propane (Tf(2)CHCH(2)CHTf(2)) is one of the most effective Brønsted acid precatalysts for the Mukaiyama aldol type reactions of sterically hindered ketones. By using Tf(2)CHCH(2)CHTf(2) in a range from 0.5 to 2.0 mol %, the vinylogous Mukaiyama aldol reaction of alpha-substituted cyclohexanones with 2-silyloxyfurans smoothly proceeded to give the aldol products in excellent yield without the loss of diastereoselectivity. Under similar conditions, acyclic ketene silyl acetals also performed as nice nucleophiles toward sterically hindered ketones. These findings suggest that Tf(2)CHCH(2)CHTf(2) induced Mukaiyama aldol type reactions can overcome the steric hindrance between reaction sites.

Remarkable rate acceleration of intramolecular Diels–Alder reaction in ionic liquids

The intramolecular Diels-Alder reaction of an ester-tethered 1,3,9-decatriene system was significantly accelerated in ionic liquids such as [emim]BF(4), [bmim]BF(4) and [bdmim]BF(4). Under the present conditions, the IMDA reaction proceeded smoothly without the use of Lewis acid catalysts to give cis-fused bicyclic lactones in good yield with high diastereoselectivity.

Direct alkylative Passerini reaction of aldehydes, isocyanides, and free aliphatic alcohols catalyzed by indium(III) triflate.

In(OTf)(3) was found to be a useful Lewis acid catalyst for direct alkylative Passerini reaction of aldehydes, isocyanides, and free aliphatic alcohols. In the present reaction, aromatic and alpha,beta-unsaturated aldehydes performed as nice substrates to give the corresponding alpha-alkoxy amide products in good yield.

Synthesis of δ-Oxo-1,1-bis(triflyl)alkanes and Their Acidities

The reaction of 1,1-bis(triflyl)ethylene generated in situ with enolizable carbonyls yielded δ-oxo-1,1-bis(triflyl)alkane derivatives. Their acidities in both the gas and solution phases were determined.

2-(Pyridinium-1-yl)-1,1-bis(perfluoroalkylsulfonyl)ethan-1-ide: A Practical Reagent for Synthesis of Strongly Acidic 1,1-Bis(perfluoroalkylsulfonyl)alkanes

On mixing (Rf SO2 )2 CH2 (Rf =perfluoroalkyl), paraformaldehyde, and substituted pyridines, a three-component reaction proceeded smoothly to give unusual zwitterions bearing both pyridinium and stabilized carbanion moieties in good to excellent yields. Of these, 2-fluoropyridinium derivatives rapidly dissociated in acetonitrile to give equilibrium mixtures of the zwitterions and (Rf SO2 )2 C=CH2 /2-fluoropyridine, as confirmed by detailed variable-temperature NMR studies. The dynamic behavior of such 2-fluoropyridinium compounds allows them to be used as shelf-stable, easy-to-handle sources of (Rf SO2 )2 C=CH2 . With these reagents, strongly acidic carbon acids (Rf SO2 )2 CHR were synthesized, which served as a new type of acid catalysts. Moreover, C-C bond-forming reactions with a ketene silyl acetal proceeded efficiently with Tf2 C=CH2 generated in situ.

Chemistry of Fluorinated Carbon Acids: Synthesis, Physicochemical Properties, and Catalysis.

The bis[(trifluoromethyl)sulfonyl]methyl (Tf2CH; Tf=SO2CF3) group is known to be one of the strongest carbon acid functionalities. The acidity of such carbon acids in the gas phase is stronger than that of sulfuric acid. Our recent investigations have demonstrated that this type of carbon acids work as novel acid catalysts. In this paper, recent achievements in carbon acid chemistry by our research group, including synthesis, physicochemical properties, and catalysis, are summarized.

Green and Catalytic Methods for γ-Lactone Synthesis

Abstract Dihydrofuran-2(3 H )-one (γ-butyrolactone) and some related γ-lactones are widely found in the structures of biologically active natural products. Such molecular structures are also used as potent building blocks in organic synthesis. In this chapter, recent achievements of γ-lactone synthesis are reviewed. In particular, catalytic methodologies directing to environment-friendly chemical processes are covered as a major topic.